O'Gara kicked the winning penalty against Leicester
Leicester: (6) 19
Pens: Burke (2), Goode (2)
Munster: (15) 21
Tries: O'Callaghan, Wallace
Pens: O'Gara (2)
Ronan O'Gara's late penalty snatched victory for champions Munster in a pulsating Heineken Cup tie with Leicester at a wet Welford Road.
Leicester had fought back from a nine-point deficit with a converted penalty try and a penalty to lead for the first time before O'Gara struck.
The Tigers, dominant in the line-out, were ultimately sunk by indiscipline.
But Munster were smarter and took their chances, with first-half tries from Donnacha O'Callaghan and David Wallace.
Munster led 15-6 at half-time, but Tigers' rally took them to 19-18 with five minutes left before O'Gara's winning kick from the halfway line in lashing rain.
Fly-half O'Gara, who apologised afterwards for his outspoken criticism of English rugby in the build-up, admitted to knocking-on as he made the break that led to the penalty.
It's a game of small margins - they took their opportunities and we obviously didn't
Leicester coach Pat Howard
The result leaves the Tigers effectively needing to win their remaining five Pool Four games - against Cardiff Blues (twice), Bourgoin (twice) and Munster away - in the quest for a quarter-final place.
From the kick-off, the importance of the match in terms of qualification was obvious as both sides thundered into it at a brutal pace.
Munster set the scoreboard ticking on nine minutes when O'Callaghan snatched a turnover on the halfway line and found himself in the clear, beating rival lock Ben Kay in a foot race to the line.
O'Gara missed the conversion and five minutes later Tigers' fly-half Paul Burke narrowed the gap with a penalty.
But O'Gara, who was packing down at number eight for the early scrums, added a drop-goal shortly after.
Leicester were looking threatening up front, in the line-out and in open play, but two quick missed penalties from Burke kept them in arrears.
The Tigers also went close after a Martin Corry break set up good field position but indiscipline let Munster off the hook, not for the first time.
The home side were made to pay as Munster added a second try five minutes into first-half injury time when Wallace finished off a break from right wing John Kelly and good link play from South African centre Trevor Halstead.
Burke kicked a penalty on the whistle to take some of the sting out, but Tigers went in on the back foot.
Tigers' coach Pat Howard swapped Burke for the superior kicking of Andy Goode and the new fly-half immediately began probing behind Munster' s line, almost setting up Daryl Gibson for a chip-through try.
Goode did slot a smart penalty from the right on 53 minutes and O'Gara's miss moments later kept Tigers six points adrift.
More Tigers indiscipline gifted Munster another three points but a bullocking charge from the Leicester pack earned them a series of five-yard scrums, and after Munster infringed too many times, the referee awarded the home side a penalty try, converted by Goode.
Leicester went ahead for the first time shortly after with a Goode penalty but with two minutes left O'Gara thumped a penalty from the halfway line to snatch victory.
Leicester coach Pat Howard:
"It's a game of small margins. We had our opportunities. They took theirs and scored two tries and we obviously didn't.
"It's unfortunate but we'll deal with it, but we've got plenty of games to go in this competition.
"We're in the same situation as Munster were a year ago when they lost their first game - there's a long way to go."
Munster fly-half Ronan O'Gara:
"It was a great win, we showed good resolve and it was important that we got our season off to a good start.
"We've been struggling in our domestic league but I think the Heineken Cup brings out the best of us.
"Today was a good start but if any side can come to Thomond Park [and win] it's Leicester."
Leicester: Vesty; G Murphy, Smith, Gibson, Varndell; Burke, Bemand; Ayerza, Chuter, Castrogiovanni; Cullen, Kay; Deacon, Moody, Corry (capt).
Replacements: Buckland, White, Crane, Jennings, Ellis, Goode, Rabeni.
Munster: Payne, Kelly, Murphy, Halstead, Dowling, O'Gara, Stringer, Horan, Sheahan, Hayes, O'Callaghan, O'Connell (capt), Leamy, Wallace, Foley.
Replacements: Kyriacou, Pucciariello, O'Driscoll, Quinlan, O'Leary, Manning, Mafi.