ATLANTA -- Jace Peterson's first walk-off homer couldn't have come at a better time for the Atlanta Braves.

Peterson hit a misplaced 3-2 slider from Shawn Kelley over the right-field fence with two outs in the 10th inning for a 7-6 victory over the Washington Nationals on Sunday.

Playing his first game in center field, Peterson made a catch while crashing into the fence early in the game and then won it with his seventh homer of the season.

"It was a fun game," Peterson said. "We needed a win, and fortunately it worked out for us."

The victory snapped a seven-game losing streak by the Braves and was just their second win over the Nationals in 13 games this season.

Kelley (1-2) got two quick outs in the 10th, then made a mistake to Peterson.

"I was totally confident walking him when it got to 3-2, so I wasn't going to give him anything good to hit," Kelley said. "But I left a slider right there in the middle of the plate."

"I've faced him in the past," Peterson said. "He's got a really good slider. Normally he's pretty consistent with his slider. Fortunately for me, he hung it was up in the zone, and I was able to put a good swing on it."

The victory snapped a seven-game losing streak by the Braves, who benefited from the Nationals' five errors. The last time Washington had committed five was in 2011, also in Atlanta.

"We didn't play a good game at all," Nationals manager Dusty Baker said. "We played a sloppy game. We'd have been lucky to win that game with five errors."

Bryce Harper hit a three-run homer in the third inning for the Nationals, and Chris Heisey had a two-run shot in the sixth inning, but the Braves scored twice in the eighth to force extra innings.

Matt Kemp led off the tying eighth-inning rally by driving a 1-1 slider from Yusmeiro Petit into the left-field seats for his 25th home run and second with Atlanta.

The Braves then loaded the bases with no outs on a single by Jeff Francoeur, a throwing error by Petit on a sacrifice bunt and an intentional walk before a downpour caused a 64-minute delay.

Blake Treinen kept the Braves from taking the lead. Gordon Beckham hit into a double play on the reliever's first pitch, although the tying run scored on the play. Dansby Swanson grounded out to end the inning.

Jose Ramirez (1-0) stranded Harper at second base in the top of the 10th after a single and stolen base to get the victory.

Harper's homer, his 22nd of the season and 16th of his career against the Braves, was a long blast to right field on a first-pitch slider from Joel De La Cruz. It was part of a four-run third inning that would have been bigger if Peterson had not made a catch while crashing into the fence.

"I knew I had a good jump on it," said Peterson, who is primarily an infielder. "I just tried to turn and really get up and catch. The wall was right there. I was able to hang onto it.

"I got the wind knocked out of me. I couldn't breathe. That was really it. I got a little bit of a bruise on the face, but other than that, everything feels good."

Nationals starter Gio Gonzalez, who was bidding for his 100th career victory, allowed six hits and four runs (three earned) in 5 2/3 innings while striking out eight and walking three. He also had the first two-hit game of his career.

The Braves benefited from two errors in the bottom of the inning to cut the Nationals' lead to 4-3. Nick Markakis' double drove in two runs.

De La Cruz became the 32nd straight Braves starter not to make it to the seventh inning. He worked 5 2/3 innings and allowed seven hits and six runs while walking two, hitting a batter and striking out four.

De La Cruz retired nine straight batters before a one-out walk in the sixth inning, and Heisey followed with his eighth homer, lining a 2-1 sinker into the left-field seats.

With his bullpen out of fresh arms near the end of a pitcher-eating road trip, Baker was left without many options.

"You hate to lose, but we didn't have any more pitching after that," Baker said. "If we'd gone any further, we would have really been in harm's way with our bullpen."

NOTES: Braves 1B Freddie Freeman got a cortisone shot in the middle finger of his right hand after Saturday's game and wasn't available for the series finale. ... RF Nick Markakis played 1B for the first time since 2014 with Baltimore and just the sixth time of his career. ... The Braves activated RHP John Gant, who had been on the disabled list since June 28 with a left oblique strain. He took the roster spot of RHP Tyrell Jenkins, demoted to Triple-A Gwinnett after giving up eight runs in the fourth inning Saturday. ... LF Jayson Werth and 3B Anthony Rendon didn't start for the Nationals. ... RHP Stephen Strasburg (15-4, 3.59 ERA) will try to bounce back from three consecutive rough starts as the Nationals open a two-game interleague series at Baltimore on Monday. ... The Braves begin a road trip at Arizona, with Mike Foltynewicz (6-5, 4.45 ERA) drawing Monday's start.