And it was a victory the visitors fully deserved. They trailed 17-13 at half time folllowing a first half injury time try from Anthony Horgan, created by a sublime Barry Murphy break, but owned the ball for the opening ten minutes of the restart.
In that period Gregor nailed a penalty after just two minutes and then, two minutes later gave his side the lead with a try which he then converted for a 23-17 lead.
Five minutes later the gap was nine when he landed his sixth successful kick leaving Munster with a mountain to climb.
A 69th minute Mossy Lawlor penalty from in front of the posts at a time when the Warriors were playing with 14 following the yellow card for winger Mike Roberts, set up a tense finale.
Munster looked to have a chance of a fourth try in the dying moments when they drove from a line-out only for the chance to disappear when the ball was knocked forward.
Munster: S Payne; J Kelly, B Murphy, T Halstead (G Connolly 79 min), A Horgan; M Lawlor, T O'Leary; F Roche, D Fogarty, F Pucciariello; D O'Callaghan, M O'Driscoll; S Keogh, J O'Connor (J O'Sullivan 50 min), A Foley (capt).