Cautious speculation surrounded the game, however, as Stephen Strasburg was removed with an apparent injury after throwing 51 pitches in the first two innings.
Strasburg worked his way out of a pair jams but racked up his pitch count and was replaced by reliever Matt Grace to start the third inning.
Brian Goodwin led off the game with a home run and the Nats tacked on three more runs in the top of the first with all nine hitters coming to the plate.
One of those hits was a single off the bat of Bryce Harper, who extended his hitting streak to a career-high 16 games.
Grace retired the first seven hitters he faced, but ran into some trouble in the fifth with the Nationals holding a 5-0 lead.
He gave up two runs and left two runners on base with one out for Joe Blanton, who got Washington out of the jam without allowing further damage.
Enny Romero pitched a scoreless sixth, but left in the top of the seventh with an undisclosed injury after giving up a two-out walk to Paul Goldschmidt.
Wilmer Difo got a run back with a solo home run in the seventh, his second of the season.
The game was then handed to Matt Albers, who got the Nats into the ninth with the score sitting at 6-2.
Sean Doolittle finished things off in the ninth, giving the Nats a 7-2 road trip.
Washington now 59-38.
More details on Strasburg and Romero coming postgame...
Here’s how it happened:
• The Nationals didn’t wait long to break out their bats. Brian Goodwin led off the game with a solo home run, crushing a no-doubter to straightaway center field.
Wilmer Difo and Bryce Harper followed with back-to-back singles. Difo came in to score when Ryan Zimmerman hit a sacrifice fly to center, and Harper moved to second on a Daniel Murphy walk.
The line kept on moving when Anthony Rendon singled up the middle, scoring Harper from second. Jose Lobaton capped off the inning with an RBI single of his own one out later, giving the Nats a 4-0 lead before Stephen Strasburg took the mound.
• Strasburg has surpassed 200 innings in a season just once in his eight-year career, but he’s managed to stay healthy through the first three and a half months of this season.
His command wasn’t as sharp as it’s been for most of this season, and he allowed two hitters to reach base in each of the two innings he pitched.
Matt Grace was seen warming up in the bullpen while the Nationals were at the plate in the top of the third, and he came in to replace Strasburg once the half inning ended.
• Stephen Strasburg’s Line: 2.0 IP, 1 H, 0 R, 3 BB, 2 Ks, 51 P, 29 S, 2/2 GO/FO
• The Nats pushed another run across in the third when they loaded the bases with no outs for Adrian Sanchez. Washington’s rookie shortstop hit a grounder up the middle that the Diamondbacks turned into a fielder’s choice, but a run crossed the plate and the Nats pushed their lead to 5-0.
• Grace was very effective during the first two innings he pitched. He retired all six batters in the third and fourth innings, but struggled to continue the momentum in the fifth. Four straight Diamondbacks reached base against him, pushing two runs across the board and forcing Dusty Baker to go to Joe Blanton to get them out of the jam.
• Robbie Ray, the former Nats’ prospect dealt to the Detroit Tigers in the Doug Fister trade, has had a strong season for Arizona but struggled against the Nationals’ bats.
He only got through five innings before being relieved in the top of the sixth.
• Robbie Ray’s Line: 5.0 IP, 6 H, 5 R, 4 ER, 2 BB, 4 Ks, 101 P, 60 Ks, 1 HR, 6/3 GO/FO
• Nats’ No. 5 prospect, according to MLB Pipeline, Andrew Stevenson made his MLB debut in the sixth, pinch hitting for Blanton. He grounded into an inning-ending fielder’s choice, but stayed in the game as Baker put him in left field and moved Difo to shortstop.
• Washington added onto their lead in the seventh when Wilmer Difo hit his second home run of the season over the wall in right center field, making it a 6-2 ballgame.
• Enny Romero came into the game in the sixth, working his way into a jam then back out of it to put a 0 on the board. He came back out for the seventh and retired the first two hitters he faced before walking Paul Goldschmidt and suffering from an apparent injury during an at-bat against J.D. Martinez. Romero would leave the game with trainers and be relieved by Matt Albers, who got the Nats out of the inning without allowing any runs to cross the plate.
• Albers stayed in and pitched a 1-2-3 eighth, then handed things over to Sean Doolittle for the final three outs. He allowed the leadoff hitter to reach, but settled in and secured the series-clinching win for Washington.