Billy Vunipola makes try-scoring comeback as Saracens beat depleted Bristol in dominant 44-23 win

Saracens 44-23 Bristol Bears: Vunipola's first appearance since fracturing his arm in June consisted of 36 minutes of carnage after George Smith was sent off for a high tackle

Vunipola's first appearance since re-fracturing his arm against South Africa in June totalled 36 minutes (Getty Images)

Billy Vunipola made a try-scoring comeback as Saracens pulled clear of Bristol in a dominant second half that underpinned a 44-23 Gallagher Premiership victory at Allianz Park.

Vunipola's first appearance since re-fracturing his arm against South Africa in June totalled 36 minutes and the injury-ravaged England number eight was a menace throughout.

Saracens needed his firepower to subdue a resilient Bristol who led 18-13 at half time and suffered the injustice of seeing George Smith harshly sent off for a tackle on Jackson Wray when the score was delicately poised at 18-18.

Smith's challenge was at shoulder height and there was a clear attempt to use his right arm, but after repeated viewings referee Andrew Jackson reached for the red card. Wray departed for a head injury assessment and was unable to return.

The Australia Test centurion stared at Jackson in disbelief, received a sympathetic pat on the head from his head coach Pat Lam upon reaching the dugout and then watched as Saracens powered clear with tries from Vunipola and Liam Williams.

England lock Maro Itoje was lucky to escape punishment for a high tackle on Joe Joyce under the posts as Bristol staged a final-quarter comeback that ended when Williams plundered two additional tries to complete his own successful return from a groin problem.

Looking to capitalise on their opening-day victory over Bath, the Bears' defence instead cracked after only four minutes with players queuing up to finish a series of forward drives until Matt Gallagher - son of All Black great John - strolled over.

It was a deceptive omen, however, as the champions were breached themselves shortly after when Callum Sheedy hoisted a high ball to the opposite wing where Alapati Leiua outjumped Alex Lewington to touch down.

Maro Itoje was lucky to stay on (Getty)

Sheedy's penalty then nudged Bristol 10-7 ahead before a thrilling passage of play saw both lines come under threat, most noticeably from Alex Goode who lit up Allianz Park with a full range of skills including a one-handed pick-up and try-saving tackle on Piers O'Connor.

An exchange of penalties between Sheedy and Farrell added to the tension as Saracens were harried at every turn, unable to seize control while conceding turnovers freely.

Farrell turned down a kick at goal to go for touch and the decision initially backfired as Bristol rallied close to their line, but another opportunity was sent between the uprights.

Once again the Bears hit back as Sione Vailanu dropped the restart to concede a scrum off which Leiua used his agility to deliver a superb finish in left corner.

Saracens attacked the third quarter with gusto and were rewarded when Goode's vision sent Lewington across the whitewash before Vunipola blasted over from a five-metre scrum.

Smith had departed and with his exit Bristol's hopes vanished, Williams scoring in the right corner to drive an additional nail into their coffin before adding his second from short range.

Nick Haining responded for the Bears, but Williams had the final say by sealing his hat-trick.

PA