MLB.com's No. 2 prospect pulled Jeurys Familia's 3-1 fastball deep down the right field line in the Syracuse Chiefs' 6-1 loss to the Buffalo Bisons in the first game of a doubleheader split on Sunday.
"I just got a pitch I could drive," the top overall pick in the 2010 Draft told the Syracuse Post-Standard. "I was finally on time on something. I was trying to put something in play and do something."
The outfielder's homer came as part of a 2-for-3 performance. It was Harper's first extra-base hit in five games and his first RBI since April 9.
Harper was held hitless with a walk in two at-bats in Game 2, dropping his average to .243 on the season. He is slugging .375 in 17 International League contests.
The 19-year-old hit a combined .297 with 17 homers and 58 RBIs in 109 games between Class A Hagerstown and Double-A Harrisburg last season.
He entered Spring Training with an outside chance of making Washington's Opening Day roster, but after missing six games to a calf injury and recording a team-high 11 Grapefruit League strikeouts, he was assigned to Triple-A.
"Hopefully this is the start of a streak and we can keep it all going," Harper told the newspaper. "It's always fun to win. We came into this season with high hopes and thought we were going to win. That's what we want to do, and that's what we're going to do. You can turn it around really quickly."
Chiefs manager Tony Beasley, who coached Harper in the Eastern League last year, added: "I thought his swings were really good. I thought he was more calm."
On Sunday, Harper's longball was not enough to keep Yunesky Maya (1-2) off the hook. The Syracuse right-hander allowed three runs -- two earned -- on seven hits and a walk over five innings.
Buffalo starter Familia (2-1) fanned eight batters and scattered four hits to earn his second victory of the season. Harper's homer accounted for the lone run against the Mets' prospect, ranked No. 90 on MLB.com's list.