Clinical Garryowen ran in four tries, three in the final quarter, to pick up a bonus point as nine-time League winners Shannon remain rooted to third-from-bottom place in the top flight.
On a blustery night, visitors Garryowen went ahead with a third minute Declan Cusack penalty. Shannon’s task grew greater in the 14th minute when head coach Stephen Keogh was sin-binned after an intervention by a touch judge.
Garryowen took advantage and three minutes later centre Corey Hircock touched down. Cusack superbly landed the conversion.
Shannon got themselves back in the contest just before half-time when scrum-half Rob Guerin touched down.
Shannon were on terms within three minutes of the restart when out-half Tadhg Bennett landed a drop goal. With 14 minutes remaining, Garryowen struck for a crucial second try when a drop goal attempt from out-half Fergal Lawlor was charged down, and Conor Hartigan touched down unopposed.
Garryowen’s backline exposed frailties in Shannon’s defence inside the final quarter with two further tries. Centre Cusack left the Shannon defence floundering as a clear path to the try-line opened up for him. Cusack also converted. And Garryowen secured a maximum five point haul within a minute when replacement Alan Gaughan touched down.
A 77th minute touchdown from Shannon prop Kevin Griffin provided scant consolation for the home supporters.
Scorers for Shannon: R Guerin, K Griffin try each, T Bennett two cons, one drop goal.
Scorers for Garryowen: D Cusack try, pen, three cons, R O’Mahony, C Hartigan, A Gaughan try each.
SHANNON: M Lawler (capt); S McNamara, R Mullane, J Clogan, M Darcy; T Bennett, R Guerin; L Hogan, J Deegan, K Griffin; D Heffernan, F Walsh; S Keogh, J Murphy, D Quinlan.
Replacements used: K O’Neill, A O’Brien, K Hanley, L Mullane, A Bennie.
GARRYOWEN: L Bourke; R O’Mahony, C Hircock, D Cusack, I Hanley; F Lawlor, N Cronin; JP Cooney, D Rowley, P O’Shea; F McKenna, D Sherry; S Buckley, C Hartigan, P Neville.
Replacements used: A Gaughan, L Viapulu, J McInerney, D Lavery, JM Griffin.
Referee: C Pollock (IRFU).