Harper was booed by the home crowd of nearly 36,000 in his first at-bat during the 8-2 win Tuesday in Washington, D.C. Nationals ace Max Scherzer struck out his former teammate on six pitches during that initial exchange.
Scherzer got Harper to strikeout once again in the third frame, with the Phillies leading 1-0 courtesy of a second inning homer from Maikel Franco. The Phillies added another run in the top of the fourth inning on a passed ball by Nationals catcher Yan Gomes.
Harper doubled for his first hit of the game in the fifth frame, but ended up stranded at second base.
He came up to the plate for his fourth at-bat in the sixth inning. The longtime Nationals slugger ripped an RBI single to left field, scoring Segrura for Philadelphia's sixth run.
Washington finally got on the board with a two-run homer from Anthony Rendon, but Harper wasn't finished doing damage against his former crew. The six-time All-Star came up to the plate for a fifth time to face Jeremy Hellickson in the top of the eighth inning.
Hellickson and Harper worked out a 2-2 even exchange before the Nationals right-handed reliever threw an 89.1 mph fastball toward the outside of the plate. Harper hammered the offering deep to right center field for a 458-foot solo bomb. Harper's third home run of the season had an exit velocity of 112 mph and a launch angle of 27 degrees, according to Statcast.
"I guess that's sports [the boos]," Harper told NBC Sports Philadelphia. "I guess that's just what [Nationals fans] felt like. That's them. I guess I know what I'm going to get into for the next 13 years."
Harper finished the day 3-for-5 with three RBIs, two strikeouts and a run scored in the win. He is now hitting .429 with three home runs and five RBIs on the season.
Harper and the Phillies face the Nationals in the second game of the two-game National League East series at 1:05 p.m. Wednesday at Nationals Park.