New Zealand lock Chris Jack scored two tries to put Saracens on the brink of qualification for the Heineken Cup quarter-finals with a stunning bonus-point victory over Biarritz.

Hugh Vyvyan and Rodd Penney also crossed while a late penalty try completed the rout as Alan Gaffney's side charged five points clear at the top of Pool Four.

Biarritz, who occupy third place in the French championship, controlled much of the first half with Romain Cabannes' try rewarding their superiority.

But Vyvyan struck deep into first-half injury time to spark Saracens' fightback and after the interval there was only one side in it as Biarritz were put to the sword.

Impressive fly-half Glen Jackson had a flawless afternoon with the boot, kicking 18 points to break the French club's resistance.

French giants Biarritz have reached the knockout stages for the last five years but that proud record looks set to be concluded this season.

Saracens now travel to Glasgow for their last pool game needing just a single match point to guarantee their passage into the quarter-finals for the first time.

Biarritz hooker Benoit August was lucky to escape a yellow card for a 12th-minute punch on Jackson with referee Nigel Owens deeming a verbal warning sufficient.

Saracens were making inroads with their line-out catch and drive and one take by Jack led to a penalty which Jackson landed.

But disaster struck in the 17th minute when Andy Farrell took too long to clear his line and Damien Traille charged down the kick with the ball spilling into the path of centre Cabannes who touched down.

Scrum-half Julien Dupuy slotted the conversion and then stretched the lead with a sweetly-struck long-range penalty.

Panic reigned in the Saracens defence in the 31st minute as Brent Russell raced back to deny Trevor Hall a chance.

Only Jackson's boot kept the scoreboard ticking over with a second penalty but Dupuy replied in kind to keep the French club in the driving seat.

Saracens finally pierced the opposition defence five minutes into first-half injury time with Farrell doing the initial damage with a useful run.

The ball was recycled to Jackson who spotted Vyvyan on his inside shoulder and the rangy second row showed strength to ride a tackle from Nicolas Brusque and crash over.

Jackson booted the conversion to level the scores at 13-13 heading into the second half.

Saracens seized the initiative two minutes after the interval with a magnificent passage of play started by prop Nick Lloyd's charge through midfield.

A host of home players were involved in the move that ended when winger Richard Haughton placed the ball over the line.

Owens went upstairs for confirmation, a shrewd decision as replays showed Haughton had lost control of the ball and Biarritz were saved.

Vyvyan almost drove over for a second time to confirm Saracens were in the ascendancy and Jackson landed his third penalty to nudge them ahead.

Biarritz had looked so strong in the first half but now their defence was being unlocked at will.

Haughton and Russell combined down the right to set up another opportunity which was finished by Jack who took advantage of the space before him to collect the ball.

It was former All-Black lock Jack's first try for Saracens since arriving at Vicarage Road in October.

Dupuy slashed the deficit with a penalty but the home side again displayed their ruthless streak to run in a third try.

Farrell took the ball on the crash but it was De Kock's smart work at the breakdown that did the damage with the skipper slipping a pass inside to Penney who weaved his way to the line.

Jackson added the conversion to send Saracens 30-16 ahead and then another penalty and to make matters worse for Biarritz, Serge Betsen was sin-binned for use of the boot.

The bonus point arrived with two minutes remaining, Jack driving through the middle for his second try.

But Saracens were not finished with an injury-time penalty try completing a famous victory.