The Washington Nationals are in the thick of a crowded playoff race for the first time in their history, entering play Thursday within shouting distance of the NL East lead while forced to fend off six teams within four and a half games of them in the Wild Card standings.

With the calendar about to turn to September, the Nationals and every other team across baseball are about to see their active rosters expand from 25 to 40. Critics complain this creates too many pitching changes and slows games down, but it also presents an opportunity for contenders to give fringe roster players a chance to prove their worth ahead of the postseason.

That’s good news for the NL East’s playoff hopefuls, all of which have suffered varying degrees of bullpen woes this season. Only a few members of each team’s relief corps should be a lock to make the postseason roster—if they get there—so September will be an important month as managers and front offices evaluate who can be depended on in big spots.

The Locks

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Braves: Luke Jackson, Shane Greene, Anthony Swarzak, Mark Melancon, Sean Newcomb

Atlanta has had a carousel of relievers compete for the ninth inning job, and although Jackson leads the team with 18 saves, he’s since been demoted from the closer role. But that’s not the worst news for Jackson, as the right-hander owns just a 4.60 ERA in the ninth this season but has been much better to the tune of a 2.38 ERA in all other innings.

Greene didn’t initially perform as expected after coming over from the Detroit Tigers in a deadline deal, allowing seven earned runs in his first 4.1 innings with team. But the 2019 All-Star has since rattled off eight straight scoreless appearances and looks like the dangerous late-inning reliever they acquired in the first place.

Melancon also joined the Braves at the trade deadline and has since been named the team’s closer, going five for five in save opportunities. Although that position is hardly safely in his grasp, Melancon is as solid a lock to make the postseason roster as anyone in the Atlanta bullpen.

The Braves traded for Swarzak in May after he got off to a rough start with the Seattle Mariners. Of Swarzak’s 34 appearances with Atlanta this season, he’s pitched the eighth inning in 22 of them. It’s safe to say the team is comfortable relying on him in late innings.

After starting 30 games last year, Newcomb made just three starts in the rotation before being sent down to the minors in mid-April. He came back up in May and has been a reliable multi-inning reliever out of the bullpen. Even though Newcomb still sees himself as a starter long term, he’s certainly impressed as a relief pitcher (3.30 ERA, 9.5 K/9) this season.

Nats: Sean Doolittle, Fernando Rodney, Daniel Hudson, Hunter Strickland, Wander Suero

Doolittle figures to be activated off the Injured List sometime this weekend and has been the team’s closer all season long. Even if he continues to struggle with fatigue down the stretch, it’d be hard to imagine the team not at least using him in a late-inning role.

Rodney has 10 holds and two saves since signing with the Nationals in late June. He’s struggled when pitching on back-to-back days but has been about as reliable as you can expect a 42-year-old who was designated for assignment earlier this season to be.

Hudson and Strickland both joined Washington at the trade deadline and have been valuable additions in the late innings, sporting 1.35 and 1.64 ERAs, respectively, since coming to D.C.

Suero has been as streaky as it gets this season, but his ability to miss bats coupled with manager Davey Martinez’s continued reliance on him during high-leverage situations makes him a solid lock to make the postseason roster.

Phillies: Hector Neris, Adam Morgan, Jose Alvarez, Mike Morin, Blake Parker

Neris has been the workhorse of the Phillies’ bullpen this season, leading the team in saves (23) and innings (55.2). He sports a 0.60 ERA since July 21 and has pitched earlier than the seventh inning just once all season. This one is a no brainer.

Ever since Morgan went down with a left flexor strain, Alvarez has been the Phillies’ primary left-hander out of the bullpen in high-leverage situations. Morgan is expected to return at some point this season, giving the Phillies two quality southpaws to lean on in later innings.

But with Tommy Hunter, David Robertson and Pat Neshek all likely missing the rest of the season, the Phillies have had to get creative with midseason additions.

Two of those arms, Morin and Parker, joined the club after the All-Star Break and have pitched well in their short time with the club. Although they might not be considered bona fide locks given how long they’ve been in the organization, Philadelphia’s reliever depth doesn’t offer many replacements who could beat them out for a playoff spot.

Mets: Edwin Diaz, Seth Lugo, Justin Wilson, Jeurys Familia, Luis Avilan

As disappointing as Diaz’s first season in New York has been, it’d be difficult to imagine the Mets deciding to cut their prized offseason addition from the postseason roster. Manager Mickey Callaway has called on other relievers in save situations as of late, so Diaz will likely be relegated to a middle-to-late-inning role if the Mets do make the postseason.

The issue for Lugo has always been his health, but ever since coming off the Injured List on May 31, he’s been New York’s most dependable reliever. He’s probably the Mets’ best option for the ninth and get this: On a team where the 2018 NL Cy Young winner headlines a stacked rotation, the only Mets player with at least 10 games and a WHIP below 1.000 is, you guessed it, Lugo.

Two IL stints limited him to just 10 appearances over the first three months of the season, but Wilson has been the team’s best left-hander out of the bullpen in the second half.

Familia, like Diaz, was signed last offseason to anchor the back end of the Mets’ bullpen. His unsightly 5.87 ERA and 1.761 WHIP show that he’s had some significant struggles this season, but he’s begun to turn things around in August. With a $6.67 million salary in 2019, it’d be very surprising if Familia was left off the playoff roster.

Avilan makes the list of locks because he’s a left-handed pitcher on a team with very little southpaw depth. The only other lefty relievers on the Mets’ 40-man are Daniel Zamora and Donnie Hart, who’ve combined for just 7.1 innings in the majors this season.

The Favorites

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Braves: Jerry Blevins, Josh Tomlin

All five of the aforementioned locks to make the Braves’ postseason roster are righties, so Blevins could prove to be an important piece on the roster given left-handed hitters are hitting just .167 against him this year.

Tomlin was originally signed to a minor-league deal but was added to major-league roster ahead of Opening Day when the Braves entered the season with a slew of injuries to their pitching staff. He’s been a solid weapon out of the ’pen but has only been used five times in the month of August, suggesting he may have lost favor in the eyes of manager Brian Snitker.

Nats: Tanner Rainey, Roenis Elias

It was very telling after the trade deadline when the Nationals designated Javy Guerra for assignment to help make room for the new arms rather than send Rainey down to the minors. Although he’s had some streaky performances, Rainey has been a pleasant surprise after being acquired in the Tanner Roark trade last offseason.

Elias only made one appearance before hitting the Injured List with a strained hamstring that he sustained while running the bases. He’s likely to be activated from the IL this weekend and holds the edge over fellow lefty Matt Grace given the latter’s continued struggles.

Phillies: Ranger Suarez, Juan Nicasio

Suarez has spent most of the season in the minors but has shown manager Gabe Kapler that he’s capable of providing more than one inning when necessary. Like the Mets, the Phillies don’t have many guys who stand out from the pack, so Suarez has a great opportunity to secure a potential postseason spot with a strong performance down the stretch.

Nicasio is on the IL with rotator cuff tendinitis in his throwing shoulder, so there’s no guarantee that he’s healthy in time for the playoffs. But the right-hander sported a 2.79 ERA over his final 11 appearances before getting hurt. If he can pick up where he left off when he returns, Nicasio stands a good chance of earning Kapler’s favor.

Mets: Paul Sewald, Brad Brach

Sewald notched his first career save earlier this month, but only after he pitched the eighth inning and rain forced the umpires to call the contest shortly afterward. He’s pitched well in nine appearances (2.57 ERA, 0.857 WHIP) but will have to prove those number are for real after he finished with a 6.07 ERA and 1.509 WHIP in 56.1 innings in 2018.

After being DFA’d by the Chicago Cubs in early August, Brach signed with the Mets and has since been used in the middle innings. He hasn’t been super impressive, but his resume as a former All-Star makes him a good candidate to rise above the rest of New York’s middling relievers.

The Fringe Guys

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Braves: Darren O’Day, Chris Martin, A.J. Minter, Chad Sobotka

O’Day has yet to throw a pitch in the majors this season but made his first rehab assignment Aug. 23 and could rejoin the club within a couple weeks.

The Braves acquired Martin from the Texas Rangers at the trade deadline in what looked like a savvy move at the time. He’s been a disappointment since joining the team but still has strong peripherals (2.18 FIP) that suggest he should return to form.

Minter (7.24 ERA) and Sobotka (5.54) are both in the minors after being optioned to make room for Atlanta’s trade deadline acquisitions. They’ll get another chance to prove themselves in September after having the chance to reset themselves away from the majors.

Nats: Javy Guerra, Matt Grace, Erick Fedde, Greg Holland

Guerra is prone to some clunkers, but he’s been often used for two or even three innings at a time when a starter exits early.

Coming off a season in which he accumulated a 2.87 ERA but a 3.39 FIP, some regression was expected for Matt Grace. However, a 6.36 ERA is certainly uncharacteristic of the lefty and he could still have a chance at a playoff spot if he turns things around in September.

Fedde is probably disappointed that he lost out on the No. 5 starter job to Joe Ross earlier this month, but he could still make the postseason by posting similar numbers as a reliever. His 3.38 ERA out of the bullpen is more than a run better than his mark (4.48) as a starter.

The big wild card here is Greg Holland, who isn’t on the team’s 40-man roster but could certainly push for a spot. Through seven appearances at Double-A Harrisburg, he has yet to allow a run.

Phillies: Seranthony Dominguez, Jared Hughes, Nick Pivetta, Jared Eickhoff, Edgar Garcia

Dominguez has been on the shelf since June 7 with a UCL injury, but the Phillies hope he can return sometime in September. If he does—which is a big if—he immediately jumps to a favorite given his previous success with the team.

Hughes has only made seven appearances with the Phillies since being claimed off waivers from the Cincinnati Reds. He’s having a down year in 2019 (4.47 ERA vs. 2.89 career average) but is just one season removed from finishing with a 1.94 mark in 78.2 innings.

Pivetta and Eickhoff have both been used predominantly as starters this season and with Jake Arrieta out for the year with bone spurs one or both could rejoin the rotation—although they would have to jump Drew Smyly, Vince Velasquez or Jason Vargas. If they come out of the bullpen, however, they would probably have a better chance of making the postseason roster.

Garcia has been used a lot this season by the Phillies, ranking among the team leaders with 29 appearances this season. But that really has been a result of necessity, as Garcia has a team-high 6.59 FIP and a staggering 5.8 BB/9. He certainly has the advantage of being a familiar face but will need to prove he can be consistent before the Phillies can consider adding him to the playoff roster.

Mets: Stephen Nogosek, Tyler Bashlor, Drew Gagnon, Walker Lockett

Nogosek may not scare anyone with his unsightly 10.80 ERA in seven appearances this year, but he’s been an entirely different pitcher at AAA-Syracuse. The 24-year-old has yet to allow a run through 21 appearances after giving up just two in 19 innings (1.89 ERA) in Double-A.

Neither Bashlor nor Gagnon impressed much in their major-league stints this season, but both have the opportunity to overtake Brach or Sewald with strong performances down the stretch. Regardless, they’re both likely candidates for September call-ups given the Mets’ need for innings eaters.

Lockett has been used a spot starter this season but will likely be relegated to the bullpen if he does get called up to the majors. With a four-seamer that tops out at 96 mph, it’ll be interesting to see if there’s an uptick in his velocity if he transitions to a relief role.

...Oh yeah. Sorry, Marlins fans.