"I was trying to battle," Harper said. "Took two good swings right there 0-0 and 0-1. Never want to get behind on a guy like that, but battled the best I could and got into a pretty good count right there and got a good pitch to hit."
It also marked Harper's second homer of the afternoon after he homered in the third inning off Phillies starter Jerad Eickhoff. Harper's heroics helped the Nationals escape with a victory they nearly gave away with some late miscues.
Washington led 3-1 when the Phillies scored twice in the eighth inning aided by an error from Jayson Werth in left field that allowed one run to score before Koda Glover surrendered a run-scoring single to tie the game at 3. Cesar Hernandez reached base four times with three hits and a walk. It spoiled a stellar performance from left-hander Gio Gonzalez, who pitched into the eighth inning for the first time since 2015, and left to a standing ovation from the 29,774 fans.
But the Nationals rallied to set the stage for Harper, who came through in a big moment.
"We made mistakes and it cost us," Nationals manager Dusty Baker said. "And then Bryce erased them."
MOMENTS THAT MATTERED Bryce walks it off: Harper's heroic moment came after he battled back from being down 0-2 to Benoit, setting up a full count. From there, Harper took a 97.1 mph fastball, Benoit's fastest pitch he's thrown all season per Statcast™, and launched it to left-center field with an exit velocity of 109.3 mph. The homer marked the third-fastest pitch Harper has hit out of a ballpark in the Statcast™ Era.
"Do you put Harper on to face Daniel Murphy?" Phillies manager Pete Mackanin said of the middle of the Nats' order. "...Those two guys back to back are tough, I don't want to see either one of them come up with the game on the line. You have to make real good pitches."
Phillies take a brief lead in the ninth: Tied 3-3 with a man on third and one out, the Phillies narrowly scratched out a go-ahead run to take a brief 4-3 lead. Freddy Galvis grounded to Murphy, who fired it home to try to cut down Altherr at the plate. But Wieters was unable to hold on as Altherr slid by him and scored what appeared to be the game's decisive run.
"I kind of got in-between," Wieters said. "I should've waited back a little bit more and had more time. But I thought it was going to be close, so I wanted to go get it, make the tag. And when you rush, you take your eye off the ball a little bit, and I just dropped it."
"I haven't seen one of those in a while." -- Gonzalez, on pitching into the eighth inning
"It's fun to watch when one of the best players in the game is locked in." -- Wieters, on Harper
"He's a special player. Obviously, he's still really young. I was telling him earlier in the game that in another four or five years he's going to be pretty good player. I think he proved me wrong once again. That was huge. Bailed us out big time." -- Werth, on Harper
INSTANT REPLAY REVIEW
In the bottom of the third inning, the Phillies challenged a call at first involving Nationals third baseman Anthony Rendon, who legged out an infield single after hitting a soft ground ball to Galvis. After a minute and 40 second review, the call on the field was confirmed and Philly lost its challenge. The call proved costly, as Harper's home run came on the very next pitch.
WHAT'S NEXT Phillies: The Phillies will enjoy an off-day Monday before heading to New York to take on the division rival Mets. Tuesday's series opener will see Zach Eflin (who will take the place of the injured Clay Buchholtz) against Mets right hander Zack Wheeler (1-1.7.45 ERA) at 7:10 p.m. ET
Nationals: Following an off-day, the Nationals will open their first ever series Tuesday at SunTrust Park in Atlanta for a 7:35 p.m. ET start against the Braves. Max Scherzer (1-1, 2.13 ERA) will take the mound after some unusual struggles with his command last time out with three wild pitches, but 10 strikeouts.
Jamal Collier covers the Nationals for MLB.com. Follow him on Twitter at @jamalcollier. Daniel Shiferaw is a contributor to MLB.com and covered the Phillies on Sunday. This story was not subject to the approval of Major League Baseball or its clubs.