Joey Carbery showed no signs of rustiness as he returned from his injury nightmare to steer Munster to a victory at the Arms Park.
Carbery came on for the final 16 minutes and set up the clinching score in the closing moments with an excellent touch-finding penalty.
Munster mauled it over to seal the issue when replacement hooker Niall Scannell touched down.
Carbery then landed the touchline conversion to really announce his return and deny Cardiff a losing bonus point.
Samoan international Ray Lee-Lo wasted little time in welcoming Carbery back for his first action in over 13 months when he smashed him in midfield, but the 25-year old showed bounced back up.
“I just told him to go out and enjoy himself, no pressure,” said Munster head coach Johann van Graan.
Cardiff led 8-6 at the break thanks to a try from lock Seb Davies but JJ Hanrahan kept the Reds in touch.
Hanrahan helped set up lock Jean Kleyn for Munster’s first try after 55 minutes with a neat dink.
Thomas missed two penalties from distance and they paid the price with Carbery’s cameo ensuring a miserable return to the Arms Park after a decade for Blues head coach Dai Young.
And then it was left to Carbery to wrap up the win which all but secures Munster’s place in the PRO14 final.
