European champions Wasps produced a storming second-half performance to begin their Heineken Cup defence in impressive fashion at the Causeway Stadium.

Lawrence Dallaglio's team trailed 12-9 at the interval, but kickers Mark Van Gisbergen and Alex King edged them ahead before England flanker Joe Worsley powered over for a 66th-minute try clincher.

Worsley's touchdown came after French international back-row forward Serge Betsen had been sin-binned, while Biarritz also finished the game with 14 men when scrum-half Dimitri Yachvili received a yellow card.

That collective loss of discipline undermined Biarritz hopes of a priceless away win, and Wasps ultimately coasted home, keeping their opponents scoreless in the second period.

Full-back Van Gisbergen finished with 14 points, and fly-half Alex King dropped two goals, with Biarritz replying through three Yachvili penalties and a Damien Traille drop-goal.

Wasps should make it two wins from two when they visit Italian minnows Calvisano next weekend, but Biarritz, Heineken Cup semi-finalists last season, face a must-win home game against twice European champions Leicester.

Wasps could hardly have encountered a tougher start to their European campaign, facing a Biarritz outfit boasting 11 internationals, including new signings Traille and Imanol Harinordoquy.

Injured skipper Thomas Lievremont missed the clash but Biarritz arrived in Wycombe with the best attacking and defensive records of any team during this season's early French Championship flurries.

Wasps welcomed back England star Josh Lewsey following his recovery from a broken hand and his fellow World Cup winner Matt Dawson also returned after hamstring problems.

Dallaglio led the Londoners into battle knowing a home victory was essential, given the significant presence of Biarritz and Leicester in their qualifying group.

The game began in dynamic fashion, with the Biarritz forwards making an immediate statement by setting up a platform from which Yachvili slotted a second-minute penalty.

Wasps, stung by the setback, roared upfield through a Lewsey break, and his fellow wing Tom Voyce looked to have scored wide out after taking hooker Phil Greening's pass, but video referee David McHugh ruled otherwise.

Biarritz enjoyed dominance during the opening quarter, highlighted by a flowing move involving backs and forwards, and Wasps found themselves hard-pressed in defence before Van Gisbergen booted an equalising penalty on 20 minutes.

Biarritz were determined to turn the screw though, and a driven lineout again had Wasps back-pedalling within five metres of their own line.

Wasps absorbed the pressure well, but Traille put Biarritz back in front with a 20-metre drop-goal before Van Gisbergen's second penalty hauled the home side level for a second time.

Undeterred, Biarritz continued to capitalise on a subdued Wasps display, and two Yachvili penalties in three minutes made it 12-6.

Wasps at last gave their supporters something to shout about as the interval approached, when Lewsey set off on a weaving run which saw him tackled by the combined efforts of Nicolas Brusque and Jimmy Marlu just three metres out.

Wasps kept their momentum going though, and a King drop-goal narrowed the deficit to three points at half-time.

Former All Blacks prop Craig Dowd made his first appearance in almost six months when he replaced Will Green on 45 minutes, having recovered from an Achilles' tendon injury, and he received a standing ovation.

Wasps desperately needed to lift their overall performance though, and Van Gisbergen came up trumps by completing his penalty hat-trick, giving the home side their first real foothold in the game.

Biarritz also displayed the first signs of technical indiscipline, and they fell behind for the first time when King rifled over his second drop-goal, before Van Gisbergen's fourth successful penalty sent Wasps into the closing quarter six points clear.

Referee Alan Lewis' patience was then stretched too far by Betsen, who grasped Wasps possession from an offside position and received a yellow card for his illegal efforts.

With a furious Betsen kicking his heels on the touchline, Wasps capitalised to create space for Worsley's clinching touchdown, and at 25-12 adrift, Biarritz faced far too tough a task.

Yachvili compounded the degree of difficulty by landing a stray boot on Wasps hooker Phil Greening - and Wasps then knew for certain that the points were safely in the bag.