PHILADELPHIA — Stephen Strasburg is healthy and pitching well again.
Washington had won eight in a row before it lost 8-5 in the second game. Tanner Roark was tagged for eight runs and 12 hits in 3 1/3 innings.
Strasburg (5-5) allowed two runs and four hits in his second consecutive solid start since returning from the disabled list. Drew Storen pitched a perfect ninth for his 23rd save.
Strasburg, the No. 1 overall pick in the 2009 draft, was sidelined by neck tightness.
"It's good to be back getting into a game and getting into a routine," he said. "My fastball command was good. Everything is off the fastball and I was locating it pretty good today."
Dan Uggla had three hits for Washington in the opener, and Michael Taylor went 2 for 4.
The traditional doubleheader was made necessary by Saturday's rainout after 1 1/2 innings. The games took a combined 6 hours, 22 minutes.
Strasburg struggled in May, going 1-3 with an 8.00 ERA in five starts, and was placed on the DL following his May 29 start. He returned last Tuesday against Atlanta and pitched five shutout innings in a 3-1 win.
He set a season-high with 113 pitches against the Phillies.
"He pitched great," manager Matt Williams said. "We stretched him to (113) pitches and he had his good fastball even in the last inning. It's nice that he's healthy. It's important for him to stretch it today and also important for our whole team."
Roark (3-3) struggled in the second game. Making his sixth start this season, Roark's ERA rose more than a point, from 3.25 to 4.34.
"He was up in the zone a little," Williams said. "He had some balls sneak through the infield. It was just not his day."
Philadelphia tied a season high for hits in an inning with six in its four-run second.
The Nationals got three back in the fourth. Clint Robinson had an RBI single before Ian Desmond connected for a mammoth 458-foot drive to center for his seventh homer.
But the Phillies scored four more in the bottom half on Maikel Franco's two-run single, Darin Ruf's RBI single and Carlos Ruiz's sacrifice fly.
"I felt good out there," Roark said. "I thought my pitches were pretty sharp. It was just one of those days."
Jose Lobaton also homered in the second game for Washington.
Philadelphia right-hander Severino Gonzalez (3-2) allowed four runs and six hits in 5 1/3 innings. He struck out seven and walked one, and interim manager Pete Mackanin earned his first win after replacing Ryne Sandberg, who resigned on Friday.
In the opener, the Nationals scored twice in the sixth. Taylor hit an RBI double off Kevin Correia (0-2) for a 2-1 lead, and the Nationals added another run when Jake Diekman's pitch bounced off the glove of catcher Cameron Rupp for a passed ball.
The Phillies got a run back in the bottom half on Jeff Francoeur's RBI single.
But the Phillies couldn't get anything else off Strasburg, who retired the side in the seventh while striking out his final two batters.
Cesar Hernandez, Franco and Cody Asche played both games for the Phillies, combining for 11 hits. Hernandez went 6 for 8.
Taylor, Danny Espinosa and Desmond played both for the Nationals. Espinosa went 0 for 9.
MORE ON MACK
Mackanin improved to 54-55 as an interim manager in his third stint in the role with the Phillies (1-2), Pirates (12-14) and Reds (41-39).
Nationals: INF Yunel Escobar (bruised left hand) returned to the lineup in the second game. He didn't play in the opener after getting hit by a pitch on Friday night. ... OF Bryce Harper (hamstring) and Denard Span (back spasms) returned for the opener. Harper had missed the previous two games while Span sat out Friday night. Neither played in the nightcap.
Nationals: After an off day, Washington opens a series at Atlanta on Tuesday with RHP Jordan Zimmermann (5-5, 3.42 ERA) facing Braves RHP Shelby Miller (5-3, 1.94 ERA).
Phillies: Philadelphia begins a four-game home series Monday night against the Brewers, with RHP Sean O'Sullivan (1-5, 5.34 ERA) opposing Milwaukee RHP Jimmy Nelson (4-8, 4.34 ERA).