NHL's Connor McDavid Rages with Chainsmokers In Vegas for 21st Bday

NHL superstar Connor McDavid is FINALLY legally allowed to drink in America ... and he celebrated by blowing it out at a Vegas nightclub -- with the guys from The Chainsmokers.

The Edmonton Oilers captain hit up XS Nightclub in the Encore hours after beating the Vegas Golden Knights in an overtime thriller ... and got the V.I.P. treatment with a massive welcoming party.

The better news for McDavid ... the Oilers don't play again until Saturday -- so he's got an entire week to celebrate (and recover) before going back to work.