PHILADELPHIA -- Bryce Harper watched and studied Stephen Strasburg for nearly 200 starts over the past seven seasons.

Maybe he picked up a few things along the way.

Harper crushed a three-run home run to left-center field in the third inning against Strasburg on Tuesday night at Citizens Bank Park, handing the Phillies a three-run lead in an eventual 10-6 loss in 10 innings to the Nationals. It was Harper’s fourth homer of the season and his second homer in four games against his former team.

“I thought we battled. I thought they battled as well,” Harper said. “I think it’s going to be like that all year long.”

Strasburg allowed a game-tying solo homer to Maikel Franco to start the third. He then walked Aaron Nola with no outs and Jean Segura with one out to send Harper to the plate with a chance to break open the game.

Harper had not homered since April 2 in Washington. Strasburg threw him a first-pitch changeup in the dirt for ball one. He followed with a 93.8 mph fastball well outside the strike zone to make the count 2-0. Harper swung hard at a changeup, then fouled another one off, both down in the zone, to even the count at 2-2.

But then Strasburg threw Harper the same exact pitch in the same exact spot as the two prior. Harper barreled this one. The 2-2 changeup left his bat at 104.3 mph, according to Statcast. It traveled a projected 399 feet.

“Stras is one of the best,” Harper said. “Being able to go up against a guy like that is always fun. I look forward to it again.”

It was the first time in baseball history that the first overall pick in the Draft homered off the first overall pick in the previous Draft. The Nationals selected Harper in the 2010 Draft and Strasburg in the 2009 Draft.

“I think it wasn’t necessarily the wrong pitch, it was just poorly executed,” Strasburg said. “Sometimes you can second guess yourself, but if I make the pitch, it’s going to have a better result.”