Croom crashed out at the semi final stage as a stoppage time goal from Alan Kehoe proved the difference.
Croom, who were efficient in front of goal throughout, led 0-8 to 0-4 at the break, but a fast start from the Tipperary champions at the beginning of the second half turned this time.
Youngster Jamie Greaves top scored in the first half with three points (one free), while Mikey Cahill (two), Mark O’Riordan, Mark Reidy and Eoin O’Farrell were all in target.
With the margin at six points, 0-8 to 0-2, Mullinahone kicked the final two points of the first half – from Eanna Ryan and Mikey O’Shea – to leave the gap at four.
Ryans goal on 33 minutes added to his pointed free and an effort from Sean Curran. This gave his side the lead but Mark Reidy put the South Limerick side ahead with a punched goal on 49 minutes.
Teenager Greaves and Ryan O’Shea pushed Croom ahead late on, but Martin Kehoe and the late goal gave Mullinahone a Munster final berth.