Michael Phelps Loses His Shirt While Partying with Diplo in Vegas

Michael Phelps was swimming in EDM this weekend -- and even though he wasn't in the water ... the dude found a reason to lose his shirt anyway.

The all-time Olympian -- who's got 23 gold medals to his name -- was on hand Saturday night at the XS Nightclub within the Wynn Las Vegas resort ... and he was in partying mood, which was only facilitated further with Diplo in the DJ booth and a packed crowd.

Mike and Diplo bro'd out behind the turntables ... and it looks like MP got so hyped, he ended up going bare-chested amid al the festivities. Maybe he was celebrating a bet on Gervonta Davis -- who won a big boxing match against Ryan Garcia earlier in the night.

Speaking of fighters ... Mr. Conor McGregor was also in attendance, and Phelps got in a battle pose with the guy. He also smiled for the camera alongside Travis Kelce!

There was even more star power in the crowd ... Sabrina Carpenter, Dixie Damelio and Loren Gray -- not to mention Michael B. Jordan, Chace Crawford, David Dobrik and others.

Of course, there were even more A-listers who were front and center for the fight itself ... these are just a handful of celebs who decided to rage after the fact at this particular club.