O'Gara's right boot helped Munster to a narrow 15-9 win in this cagey clash with Saracens at Thomond Park.
O'Gara had a five-from-five kicking return, whereas his young counterpart Owen Farrell missed four of his seven shots at the posts.
Farrell redeemed himself by converting a 79th minute penalty for a losing bonus point which keeps Saracens at the top of Pool 1, albeit with Munster now level on 10 points ahead of next week's return fixture in Watford.
Harlequins remain on course for top spot in Pool Three after a comprehensive 57-14 victory over Zebre in Parma.
The Aviva Premiership pacesetters ran in eight tries to secure a winning bonus point.
Sam Smith scored a brace with Nick Easter, Matt Hopper, Rob Buchanan and Ben Botica also among the scorers for Connor O'Shea's high fliers, who also managed two scrum penalty tries.
The most Zebre could manage on a bitterly cold day was a first-half breakaway try by Leonardo Sarto and a late consolation for Alberto Chillon.
Toulouse put the Ospreys to the sword 30-14 with a rampant second-half performance to take control of Pool Two in the Heineken Cup.
The four-time winners led just 12-7 at the interval thanks to quick-fire tries from Florian Fritz and Yannick Nyanga.
The Ospreys hit back with a try from Kahn Fotuali'i but the second half was a one-team affair as Vincent Clerc, Census Johnson, Yoann Huget all crossed over.
The visitors again responded with a try, this time from Ryan Bevington, but it was too little too late.
Outside-half Gareth Steenson kicked 17 points as Exeter secured their first-ever win in the competition with a Pool 5 22-16 success over Scarlets at Parc y Scarlets.
Scrum-half Haydn Thomas gave the visitors the perfect start with a try on five minutes and the Chiefs led throughout from there on.
The Scarlets, who saw Wales fly-half Rhys Priestland carried from the field with an ankle injury in the second half, did grab back a late penalty try from a scrum but it was not enough as they crashed to a third straight European defeat.
Jonny Wilkinson's Toulon made it three wins out of three in Pool Six but did little to justify their tag of favourites with an unconvincing 17-6 success against struggling Sale.
Filthy conditions at the Salford City Stadium did much to bridge the gulf in class between a star-studded side leading the French Top 14 and one propping up the Aviva Premiership, but the visitors did just enough to secure the crucial points, with winger David Smith scoring the only try and Wilkinson kicking four penalties from seven attempts.
Racing Metro kept their hopes alive with a hard fought 19-9 victory over Edinburgh at Stade Yves du Manoir.
Tries from Juan Jose Imhoff and Eddy Ben Arous either side of the interval proved the difference as the Scottish outfit remained winless in the competition.
Edinburgh stay bottom of Pool One, with no points to their name, but they restored some pride with the committed performance.
Glasgow saw their hopes extinguished in the other match in Pool Four as they failed to get the bonus point win they needed as Castres won 9-6.
The match was a poor advert for European rugby - one of brutal frontal assaults relieved by long kicks and penalty awards and was little reward for the 3,348 spectators who turned up on a freezing night.
Ultimately it was decided by the boot with three successful penalties from Castres' Rory Kockott outdoing the pair from Glasgow's Scott Wight.
Fetu'u Vainikolo's try helped Connacht to a 22-14 victory over Biarritz at the Galway Sportsground in Pool Three.
The Tongan winger's first-half try was supplemented by 17 points from Dan Parks' boot to keep the Irish province in contention for a maiden appearance in the last eight of Europe's premier club competition.
Biarritz skipper Imanol Harinordoquy scored his side's only try of the match with Dimitri Yachvili kicking the other points.
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