O'Gara injured his right knee after a collision with Jamie Ringer and he has been ruled out of Munster's plans for the game against Biarritz next weekend.
Munster however responded in the best possible fashion to the loss of their first choice 10 with a gutsy second half performance that yielded three tries, all converted by Paul Burke. Burke had perhaps his best performance of the season controlling the possession that his forwards worked so hard to get and keeping the Dragon's defence honest with the odd little sniping break.
Munster backs and forwards combined well to carve out a victory that ensures Alan Gaffney's squad runner up spot in the league, a home quarter final in the Celtic Cup, and number one Irish seeding for next season's Heineken Cup.
It was only the third time that the Dragons had been beaten at home this season - they lost to Newcastle in the Heineken Cup and Edinburgh in the Celtic League - and they included in their side Grand slam heroes, Kevin Morgan, Ceri Sweeney, Ian Gough and number 8 Michael Owen.
The Welsh side also had the RBS Six Nations trophy on hand to parade before the 6,000+ crowd.
The sides were tied three points apiece at the break but it was the Munstermen who were the more committed in the second half.
Alan Quinlan capped an overall impressive performance with his side's opening try which was followed by a second from John Kelly who did exceptionally well to pick up a loose ball at pace and score to the right of the posts.
The third try came when Shaun Payne won the race to a Burke kick-through, a score that put the game beyond the home side's and Munster in fact might have had the bonus when Kelly and then replacement Stephen Keogh made inroads into the Dragons 22 only to be hauled down by last ditch defence.