WITH three minutes remaining it looked as if Young Munster had been given an AIL division one lifeline when referee Michael Black awarded them a penalty just left of the posts and inside the 22.
Had Mark Connolly landed the kick the four league points would have been welcomed enthusiastically by the home support but the ball swung an inch in the wind, cracked off the upright and was cleared to safety by St Mary's out-half Sean McCarthy.
Young Munster led 6-0 after 15 minutes thanks to a brace of penalties from the boot of Mark Connolly but St Mary's responded on 27 minutes when Barry Lynn landed a similar effort after the home side had lost Darragh Payne to the sin bin.
Four minutes before the break the Saints got the crucial score when centre Conor Donohue finished off a good backline move to give his side a 6-8 lead at the break.
Four minutes after the re-start Mark Connolly restored the home side's lead when he landed his third successful kick at the posts but on 66 minutes St Mary's snatched victory when Sean McCarthy converted a penalty from close to the touchline.