WASHINGTON -- Another strong outing from consistent right-hander Tanner Roark helped the Washington Nationals secure a three-game series victory against the Atlanta Braves on Sunday.

Roark pitched seven strong innings, Anthony Rendon hit a three-run homer and Bryce Harper had an RBI double in his first game in more than a week as the Nationals routed the Braves 9-1.

Roark (13-6) scattered five hits while yielding one run. He is two victories shy of his career high, set in 2014.

"I feel like I've learned a lot more since then, since '14 and '15 as well," Roark said. "Learning how to pitch and knowing what pitches are in the right sequence and knowing what the hitters don't handle well. You have the intellect of reading swings and what they think is coming next and you have to outsmart them. You have to be one step ahead of everybody."

The Nationals (69-47), who went 5-3 on their homestand, are now a season-high 22 games over .500. Washington maintained an 8 1/2-game lead over Miami in the National League East.

Rookie Tyrell Jenkins (2-3) allowed seven runs in 4 2/3 innings for Atlanta (44-74), which went 5-5 on its three-city road trip and has dropped 16 of its last 17 games in Washington.

Jenkins appeared to settle in after a rough first inning, at one point retiring nine in a row. But he found trouble in the fifth, and Rendon chased him with a home run to left into the Braves bullpen to give Washington a 7-1 lead.

"You feel like you're (down) 4-1, three runs, get this next guy out and come in and you may get a win," Atlanta manager Brian Snitker said. "For me, that was the big blow."

Harper was not in the Nationals' original lineup, but was inserted in his customary spot in right field about 90 minutes before the game. The defending National League MVP had not played since Aug. 6 because of a stiff neck, missing five consecutive games.

"I was going to give him another day (off), but he came in and told me he wanted to play," Nationals manager Dusty Baker said. "I told him no and he told me 'Please.' How do you tell a grown man (no) that says so politely that he wants to play? So I put him back in the lineup. He actually sounded like a little kid when he said so and you know I'm partial to kids sometimes."

Harper delivered an RBI double in his first at-bat as part of Washington's three-run first inning and later scored after walking in the fifth. He was 1-for-3 on the day.

"I was just trying to stay on the pitch up there and felt pretty good up there considering (I hadn't played) all week," Harper said.

Roark won his fourth consecutive start for the Nationals and continued his long-time mastery of Atlanta. The right-hander is 2-0 with a 0.64 ERA against the Braves in two starts this season, and is 5-1 with a 1.73 ERA in 14 career appearances against the division rival.

"I remember when they called him up when I was here before (as a coach)," Snitker said. "It seems like every time I've seen the guy pitch against us, he's been really, really good."

The Nationals quickly pounced on Jenkins, scoring three runs in the first inning. After Trea Turner led off with a double, Ben Revere laid down a bunt that Atlanta catcher Anthony Recker threw down the right-field line. Turner came around to score and Revere was credited with a single.

Harper then made his first plate appearance in more than a week and laced a double to left that scored Revere. After Wilson Ramos' groundout, Harper scored on Rendon's sacrifice fly to center.

The Braves got one back in the third inning when Ender Inciarte doubled with one out and scored on Erick Aybar's single to left. But Roark erased Aybar on a double-play grounder to prevent Atlanta from mustering a more sustained rally.

Washington bumped its lead to 4-1 when it loaded the bases with one out in the fifth inning, a rally set up by a leadoff walk to Roark. After a Ramos sacrifice fly, Rendon connected for his 15th home run of the season to expand the advantage.

"I wasn't trying to walk him, and once that happened it kind of went downhill from there," Jenkins said. "It's something that can't happen and it's something I have to work on."

Ramos added an RBI single in the seventh off Atlanta reliever Eric O'Flaherty, and Chris Heisey completed the scoring with a solo homer off Ryan Weber in the eighth.

"It was just one of them days," Snitker said. "You can't get behind and come back every day. It will kind of wear at you, too."

NOTES: Washington RF Bryce Harper returned to the starting lineup Sunday after a five-game absence due to a neck injury. ... Nationals INF Daniel Murphy was out of the lineup for the first time since July 31, while OF Jayson Werth also got a breather. Clint Robinson drew the start at first base, where Murphy played eight of the previous nine games, and Chris Heisey started in left. ... Atlanta 1B Freddie Freeman homered in the first two games of the series to give him 23 on the season, tying his career-best. Freeman also hit 23 home runs in 2012 and 2013. ... Braves 2B Jace Peterson, who is 1-for-13 lifetime against Nationals starter Tanner Roark, was out of the lineup for the first time in this series. ... After a day off Monday, the Braves begin a two-game set at home against Minnesota on Tuesday. RHP Joel De La Cruz (0-5, 4.09 ERA) will start the series opener. ... The Nationals begin a nine-game road trip Monday at Colorado. RHP Max Scherzer (12-7, 2.80 ERA) starts the opener of the three-game series at Coors Field.