Luka Doncic might have lost his Mavericks game on his 21st birthday ... but he DEFINITELY won the after party!!!
TMZ Sports has learned the NBA superstar got after it Friday night for his B-day despite losing to the Heat ... hitting up Miami hot spots with his Mavs teammates and other celebs.
We're told Doncic and the guys got dinner at Papi Steak in Miami Beach before ultimately spending the night at Club LIV.
And, you can see in photos we obtained of the festivities ... Doncic was having a blast -- even at one point getting some partying in with Bad Bunny!