Garryowen ran out comfortable winners in the first of their back-to-back clashes with local rivals Shannon, picking up a deserved bonus point at Thomond Park.
Influential centre Declan Cusack was man-of-the-match for the Light Blues. He scored a try, kicked three conversions and a penalty as Shannon were punished for slack defending in the second half.
Cusack landed his penalty after three minutes and Shannon suffered another blow on the quarter hour when player-coach Stephen Keogh was sin-binned.
Keogh received a yellow card after New Zealand referee Chris Pollock, who will be in charge of the Ireland v Scotland Six Nations match next week, had consulted with one of his touch judges.
Garryowen capitalised on their numerical advantage and a great break by Ronan O'Mahony sent the equally speedy Corey Hircock in for a try which Cusack converted.
Just on half-time, Shannon's inspirational back rower David Quinlan set up scrum half Rob Guerin for a try which Tadhg Bennett.
Out-half Bennett converted and he also dropped a goal two minutes into the second half to tie these great rivals up at 10-10.
By this stage Shannon had the benefit of the very strong wind and it looked as if they might go on and notch an elusive Division 1A win.
But it was Garryowen who crucially struck for the next score. Shannon blocked down an attempted drop goal and openside flanker Conor Hartigan was played onside and he gobbled up the ball for a Cusack converted-score.
Hartigan's 66th-minute effort was a key score and worse followed for the hosts when the Munster-capped Cusack waltzed in for his own seven-pointer just five minutes later.
Shortly afterwards, Garryowen replacement and Munster Under-19 centre James McInerney wrapped it up for the visitors with their bonus point try – just their second in 13 league games this season.
It was three minutes from the end when prop Kevin Griffin touched down for Shannon's second converted try of a night when they suffered their eighth loss of the campaign.
Referee: Chris Pollock (New Zealand)