Harper signed the largest contract in sports history [at the time] last month, securing a guaranteed $330million [£251.128m] deal across 12 years.
On Tuesday night, the megastar returned to Nationals Field for the first time since making the move, and was mocked ruthlessly by the home fans.
As he stepped up to the plate for the first time, Harper was met with chants of “T-R-A-I-T-O-R!” from Nats fans.
Then, the worst thing possible happened, as he was struck out by Max Scherzer.
Harper was hit with a low curveball that he failed to hit for the final strike, as fans were sent into pandemonium in the stands, while Harper trudged back to the dugout.
The Nationals’ Twitter account took the opportunity to aim a cheeky jab at Harper, posting the video with the caption “Yo homes, smell ya later.”
That was a reference to Harper’s new choice of walk-on music – the theme from ‘The Fresh Prince of Bel-Air’.
Harper had the last laugh, however, as he scored an incredible home run in the top of the eighth to all-but secure victory for the Phillies.
As he walked off the mound after the shot, he threw his bat up in the air as the travelling Phillies fans went crazy in the stands.
Speaking before the game, the 26-year-old Las Vegas native had paid tribute to the Nats fans and said he hoped for peace when he took to the mound.
“Of course, I think there’ll be some boos and things like that,” he said in his pre-game press conference.
“It’s part of the game.
“I think there’ll be some cheers as well.
“I’ll always remember the memories we had here, the excitement and all the screams and cheers.
“I’ll always remember that.”