Harper hit a 1-1 pitch from Atlanta reliever Jesse Biddle into the right-field seats for a solo homer in the bottom of the seventh inning Saturday in Philadelphia, extending the Phillies' lead to 7-4.
Fans gave Harper a standing ovation and chanted "MVP! MVP!''
"That's one of my favorite homers I've ever had, definitely," Harper said after Philadelphia's 8-6 win. "What a team win today. We've been swinging the bats really well as a club; and Pivetta went out there and did his job, bullpen came in, did their job. Huge homer by Franco again, huge homer by Realmuto. One through nine, just everybody grinding, everybody playing together, and that's what it's all about."
The ball traveled 465 feet -- Harper's second-longest homer since Statcast started tracking their distances in 2015.
While with the Nationals, he hit a 473-foot shot on May 4, 2018, against the Phillies.
Harper now has eight home runs of 450 feet or longer since 2015, tied for the seventh most in the majors.
In his Phillies debut Thursday, Harper went 0-for-3 with a walk, and Saturday he had gone 0-for-2 with a walk before his home run.
The Phillies improved to 2-0 with the win, and Harper said he's having fun two games into his 13-year contract with the team.
"We just go out there and try to grind as a team every single day," Harper said. "And this crowd came out, supported us today, yesterday -- Thursday, whatever it was -- and what a team. It's so much fun in that clubhouse, so much fun in this dugout. And that's what it's all about."