Travis Kelce just took the stage at Studio 8H ... and the Kansas City Chiefs superstar crushed his "Saturday Night Live" monologue -- hilariously mocking Patrick Mahomes in the process.
Kelce -- wearing a sharp double-breasted suit -- had the crowd laughing from start to finish ... with jokes about getting busted for weed in college, his infamous dating show, his QB's unique voice and, of course, beating his older brother, Jason, in the Super Bowl.
The Philadelphia Eagles star was in the front row for the whole thing .