A customer stabbed an Upper East Side bartender early yesterday after he was thrown out, police said.

The 33-year-old bartender at Brady’s Bar on Second Avenue near 82nd Street told cops he threw out the boozy troublemaker at around 2 a.m., and then was attacked by him when the employee left the pub at around 5:40.

The assailant stabbed the bartender twice in the back with an unknown object before fleeing, cops said.