Substitute Ryan Guy grabbed a crucial goal as St Patrick's Athletic maintained their European push.
A depleted Galway carved several chances before Guy's crisp 67th minute finish punished a defensive lapse in concentration.
Alan Murphy and Vinny Faherty squandered opportunities for the home side, but Guy provided the ice cool finish after his introduction when steering the ball home from close range following Keith Fahey's right wing cross.
Galway had Regillio Nootimer red carded for a foul on Glen Fitzpatrick, but Gary O'Neill missed the subsequent penalty after 87 minutes.
After suffering a cruel FAI Cup defeat to Bohemians on Monday St Patrick's were under pressure to deliver a win. Having managed six points in their last three games the Dubliners entered the Dyke Road venue armed with a degree of confidence considering Galway's suspension crisis.
Regulars Wes Charles, John Lester, Derek O'Brien, and Stephen O'Flynn were all ruled out ensuring Tony Cousins was forced to alter his starting significantly. Despite missing so many players the stakes were still piled high for relegation threatened Galway, who required a positive result.
Admirably United settled well and carved chances as Alan Murphy occupied a central role in the home side's encouraging start.
Shane Tracy drilled over after 13 minutes, and Murphy ought to have scored when clean through following Vinny Faherty's deft header.
But Pat's enjoyed one small pocket of dominance forcing four corners in quick succession, while Mark Quigley also headed a Keith Fahey cross wide.
Galway regained the imitative, and Ciaran Foley's effort crept just over the crossbar moments later, but the teams departed deadlocked at the interval.
The only goal arrived with 23 minutes left on the clock and Pat's managed to close the deal.