Heineken Cup quarter-finalists Munster suffered a shock defeat against RaboDirect PRO12 strugglers Aironi in Italy.
Despite finishing strongly, the Irish heavyweights never recovered from a 15-3 interval deficit.
Aironi, bottom of the table, turned league form on its head as they sent second-placed Munster crashing.
It was only the home side's fourth victory of the season, but one they deserved after first-half tries by flanker Nicola Cattina and centre Gabriel Pizarro underpinned a comfortable advantage.
Munster, who were without their sizeable Six Nations contingent, managed only a Scott Deasy penalty in reply as Aironi made the most of their attacking opportunities.
Munster eventually stirred in the final quarter, collecting a penalty try and touchdown from centre Lifeimi Mafi, yet it was a case of too little, too late.