An Adam Larkin penalty with the last kick of the game sent Munster crashing to their fourth defeat in a row in this Celtic League tie in Cork.
Munster had looked like stopping the rot when Jeremy Staunton had kicked them into contention with three second-half penalties to turn around a 13-6 half-time deficit and edge the home side in front with time running out.
But Ulster went on the attack one last time and set up Larkin for his pressure kick in the eighth minute of injury time.
Munster had lost captain Jim Williams to a calf injury before kick-off, but took a 6-0 lead through Staunton’s penalties and saw Ulster lose prop Ronan McCormack to the sin-bin for a deliberate offside.
But Larkin quickly reduced the deficit with a penalty and Ulster skipper Andy Ward set up centre Seamus Mallon for a try close to the posts which Larkin converted to turn the game on its head.
Larkin sent over a penalty deep into first-half injury time and Ulster were 13-6 ahead at half-time.
The Ulster fly-half lost his touch after the break with three missed penalties as Staunton kept Munster in the game.
He looked to have given them victory as the tie moved into injury time, slotting over a penalty from wide on the left but it still left Larkin with the time to give the visitors victory.