Fernando Tatis Jr.'s first homer of 2023 didn't go as well as he would have liked ... he was booed as he rounded the bases -- and then the pitcher who served it up straight up called him a "cheater."
The San Diego Padres star hit the dinger on Wednesday night while down in the minor leagues as he continues to serve his 80-game ban for his positive PED test last season.
The 24-year-old, playing for the El Paso Chihuahuas against the Sacramento River Cats, smacked the baseball deep over the left field wall ... and seemed rather impressed by the tater.
He watched it fly -- then skipped around the bases ... but there weren't many outside of him at the Northern California ballpark who were thrilled to see it.
**cheater hits a homerun on a rehab assignment during a steroid suspension** https://t.co/1gTgo9Pa8a
— Kade McClure (@kademcc) April 6, 2023
Check out video of the blast -- he was booed loudly as he came home ... and then following the game, the S.F. Giants prospect who threw the pitch took to social media to rip the guy.
"**cheater hits a homerun on a rehab assignment during a steroid suspension**," the pitcher, Kade McClure, wrote.
McClure -- a 27-year-old righty who was picked in the sixth round of the 2017 MLB draft -- didn't back down from the comment ... later appearing to prod Padres fans who were in his mentions.
Of course, Tatis Jr. is going to have to get used to this ... he'll likely face jeers at every park he plays in this year -- after the MLB said he ingested the banned substance Clostebol, considered a performance-enhancing drug, last season.