Gavin Henson's comeback was put on hold as Ospreys ran in five tries, two of them from Adrian Cashmore, against Bristol in the Powergen Cup.

Wales centre Henson, who has not played since being concussed while playing for the British Lions against the All Blacks in July, failed a late fitness test after suffering back spasms.

But Ospreys, who had already lost to Bath and Gloucester, were strong enough to see off Bristol's challenge despite a despite a hat-trick of tries from Marko Stanojevic for the home side.

There was nothing riding on the result of this game - Bath having already booked a semi-finals spot with their win over Gloucester - so both sides rested many senior players.

Bristol retained just Vaughan Going from their victory over Premiership leaders Sale a week ago.

Bristol opted to kick two early simple penalties to touch as they looked for maximum points and they opened their account after 12 minutes when Stanojevic came off his left wing to take a long pass at outside centre when inside his own half.

He drew the initial defender before passing out to full-back Going who in turn fed Lee Robinson. The right wing stepped inside to run round behind the posts before touching down with fly-half Tommy Hayes, on his Bristol debut, adding the extras.

Midway through the half the three combined for a second try with Stanojevic, the former Italian Sevens player, bursting down his own left touchline to score with Hayes converting from out wide.

Just before the half hour Ospreys fly-half Shaun Connor kicked a penalty from out on the left.

Then Ospreys full-back Cashmore sold a couple of dummies and, finding a gap between Going and scrum-half Jake Rauluni opening up in front of him, ploughed through it to claim a try that was converted by Connor from close to the left touchline.

Connor then added a penalty while opposite number Hayes saw his attempt fall short.

Then, on the stroke of half-time, replacement centre Damian Karauna intercepted a pass from openside flanker Chris Morgan and raced 55 metres for the Ospreys' second try.

Connor's conversion gave Ospreys a 20-14 interval lead but Bristol went back in front five minutes in to the second half as Robinson gave a long pass out to Stanojevic who sprinted 30 metres to the line and, despite the efforts of wing Richard Mustoe, dived over the line with Hayes converting for a 21-20 advantage.

Bristol's lead was shortlived as Connor aimed a long kick to the right corner and Cashmore managed to get the touchdown for his second try.

Connor failed to convert from the touchline and Ospreys led 25-21.

Bristol hit back immediately with Stanojevic breaking from the half-way line to complete his hat-trick of tries. Hayes converted and Bristol were back in front at 28-25.

But it proved to be Bristol's last points of the afternoon.

Connor levelled the scores with his third penalty of the game and his fourth, from 40 metres, edged the visitors back in front.

Ospreys stretched their lead with openside flanker Steven Tandy scoring in the right corner, from a front of lineout peel.

Replacement kicker Matthew Jones was off target but he found his mark a couple of minutes after a try from blindside flanker James Bater when a ball to the back of the lineout caught out Bristol.