It was Harper's sixth homer in three games -- and it lifted the Nationals to 16-15, above .500 for the first time this season.
"He's the hottest player in the world right now," said Atlanta reliever Cody Martin -- Harper's latest victim. "He's putting good swings on everything, he's seeing the ball well, his balance is good. You can't really do any one thing to him that's going to get him out. I think you just have to keep mixing it up, and that just wasn't the right pitch there, I guess.
After the victory, manager Matt Williams was asked if he had ever seen a player go on a home run tear like Harper. Williams was quick to answer and mentioned former teammate Barry Bonds, who was ahead of Williams in the Giants' lineup in the early- to mid-1990s.
Still, Williams has admired what Harper has done the last three games, going 8-for-12 (.667) with six home runs and 12 RBIs. Harper became the first player to hit six home runs in three games since Hee-Seop Choi did it with the Los Angeles Dodgers from June 10-12, 2005.
"It's really good. He is taken what they give him," Williams said. "Today, he hit a single the other way that was kind of down and off the plate. It was an offspeed pitch he hit in the last inning there. He is doing everything well."
Teammate Ian Desmond said that Harper has handled all the attention in a humble manner.
"It couldn't be happening to a better guy," Desmond said. "He is doing really well, he is handling it well, he is carrying himself humbly. It's really fun to watch."
This time, the Nationals saw a five-run lead evaporate in the late innings, but Harper's walk-off picked them up. It was the third walk-off homer of his career.
With a runner on first and Martin on the mound, Harper swung at a 1-0 pitch and hit the ball over the right-center-field wall to end the game.
"I thought I wanted to work in," Martin said. "I threw the first pitch in -- it was a bad pitch, not much purpose to it, but then a slider away, I thought maybe he'd take that and try to get a fastball, but it was a good piece of hitting."
Harper is doing more than just hitting home runs. He is playing great defense in right field. In the seventh inning, for example, the Braves had a runner on second, when Nick Markakis hit a ball to deep right field. The ball was over Harper's head, but he managed to make a nice running catch to end the inning.
"I'm working on everything," Harper said. "Not only being good offensively, trying to be the best right fielder in the game. Plain and simple. I want to play hard every single day. I want to make the play for my pitcher. If I'm helping them out, that's what I'm going to do."