The Ulster flanker was driven over seven minutes in injury time as Mick Galwey's side slipped to their second defeat of the campaign - having led 12-0 at half-time.

Fly-half David Delaney cracked over four first half penalties to see the Limerick men into their lead.

Two more Delaney efforts on 51 and 63 minutes seemed to point to an easy Shannon win, but Andre Bester's outfit were determined to avenge last season's semi-final defeat, and did so in style.

With Shannon prop Tony Buckley sin-binned on 65 minutes for persistent ruck infringing, two minutes later Ian Humphreys sliced through the cover to touch down and begin the 'Quins' comeback.

WP Strauss converted and added the extras to number eight Stuart Lamb's pushover effort for an 18-14 deficit.

Despite a dogged defensive effort, Shannon conceded a crucial third to Mustchin, whose side now lie just a point behind the Limerick men in sixth.

Scorers:

Harlequins: Tries: Ian Humphreys, Stuart Lamb, Matt Mustchin; Cons: WP Strauss 2

Shannon: Pens: David Delaney 6