The 27-year-old fly-half played his first 80 minutes of rugby in the Lansdowne Road decider since damaging his right knee ligaments against the Dragons on March 25.
And the Corkman, who displayed no ill effects ahead of his second British & Irish Lions tour next month, notched a full house of points in the first half as he added a 34th-minute drop goal to an earlier penalty, try and two conversions.
"Having been on the sidelines, I've a great hunger for the game now. I've been lucky with injuries over the last six or seven years - there's only really been three or four weeks that I've missed, here and there," said a jubilant O'Gara.
"Right now, the thought of going on the Lions tour really excites me. My injury was a bad one but all credit to Ger Hartmann (physio) for getting it right. I'm a lot more stable in my lower half."