Harris made another highlight catch, used his speed to manufacture a run and finally ended a 12-inning game against the Blue Jays with a two-run blast to right field.
A night after Adam Dunn hit a game-winning single in the 11th inning, Harris' shot gave the Nationals a 5-3 victory -- their season-best fourth straight.
"We don't want to go 11, 12, 13 innings, but [we'll do it] whenever we can get a timely hit and get a 'W,'" Harris said.
In the fifth inning, Harris hit a ground-rule double then reached third uncontested on a stolen base, as he used in-game scouting to read that pitcher Brett Cecil would only look him back once.
The stolen base was significant, as Harris scored the game's first run on a Wil Nieves sacrifice fly.
The inning before that, Harris, playing in center field, raced to a Raul Chavez line drive and sprawled out to prevent what would have been a hit to put two runners on with no outs.
"It's just getting good reads and good jumps," Harris said. "I'm thankful that I was able to make the play. I just wish I could have saw it, because the ball was in the lights the whole time."
That defense helped rookie Ross Detwiler get through seven innings, while giving up just a run on a Vernon Wells homer. He was later charged with a second run when he left an eventual scorer on base in the eighth.
After Wells' dinger tied the game in the top of the sixth, the Nationals got two runs back in the bottom half, as Cristian Guzman, Nick Johnson and Elijah Dukes all doubled.
Johnson, who walked and a singled in his first two at-bats, reached base for the 10th consecutive plate appearance to tie a franchise record dating back to 1969.
"I've been getting on base for the team, and that's how you score runs -- get on base," Johnson said. "Just trying to take consistent at-bats and swing at strikes -- have a plan."
With a 3-1 lead, Detwiler -- whom manager Manny Acta said "did a fantastic job" -- trotted out to pitch the eighth. But the first batter he faced, pinch-hitter Jose Bautist, singled to end Detwiler's night.
With the Nationals holding a 3-1 lead and a chance for Detwiler to pick up his first Major League win, Acta called for Kip Wells to replace the youngster.
But Bautista scored on an Aaron Hill single, and Hill went to second when left fielder Dunn overthrew the cutoff man. After Hill went to third on a passed ball, he touched home to tie the score at 3 on a Scott Rolen single off Joel Hanrahan.
"I felt real bad for the kid, because he deserved to win the ballgame today," Acta said.
"It's a win for the team, so you can't go wrong with that," Detwiler said.
After recently finding some consistency, the bullpen inconsistency had reared its ugly head once again. This time it was only temporary.
The 'pen bounced back to pitch scoreless ninth through 12th innings, holding the Jays at bay until Harris' walk-off pop.
Closer Mike MacDougal mowed hitters down in the ninth and 10th, and after Jesus Colome retired one batter and exited with a strained quadriceps muscle, Julian Tavarez finished off the 11th and 12th to earn his third win this season.
MacDougal and Tavarez "saved our day," Acta said.
Yet it was Harris who got the day started and kept it going for the Nationals. He is quickly becoming a fan-favorite, and game-winning home runs and diving catches only spread his reputation.
"In my heart, I'm an everyday player, but on my contract, I'm a utility guy," Harris said "Whenever I'm out there, I'm gonna try to put together a professional at-bat, play defense hard and do everything the right way."