Bristol's hopes of a priceless Heineken Cup away win were dashed by an outstanding Cardiff fightback as the Blues prevailed at the Arms Park.

Cardiff wiped out a 13-3 deficit, racing 34-13 ahead through tries by centre Jamie Robinson, flanker Maama Molitika and his back-row colleague Martyn Williams - who touched down twice.

Full-back Ben Blair chipped in with 14 points from the boot, and Bristol could only reflect on why everything unravelled so spectacularly - despite having the last word with wing Tom Arscott's consolation score.

They occupied the driving seat throughout the first half - using their forwards to impressive effect and establishing a healthy lead courtesy of full-back David Hill's try, plus two Jason Strange penalties and a conversion.

Cardiff, though, surged to a bonus-point success that sets them up nicely for next Saturday's Pool Three trip to Harlequins.

But Bristol now find themselves having to beat Memorial Stadium visitors Stade Francais - the French champions and this season's Heineken Cup favourites - 24 hours later to effectively stay afloat.

The scale of their deterioration - Bristol looked a shadow of the side that secured Heineken Cup qualification last term - will concern coaches Richard Hill and John Brain.

Cardiff, however, could not care less - having got their European campaign off to a flying start after under-achieving in the competition for so long.

The Blues were without injured fly-half Nicky Robinson, which meant a Heineken Cup debut for Dai Flanagan, and Gareth Thomas moved to the wing as Blues boss David Young fielded a midfield combination of Robinson and Tom Shanklin.

Bristol welcomed back England World Cup hooker Mark Regan, with former Blues player Nathan Budgett switched to the second row alongside New Zealander Sean Hohneck.

The west country club immediately announced their intentions, looking to play through their forwards and frustrate Cardiff at source.

Strange's opening penalty gave them a ninth-minute lead, but only after Blues wing Tom James saw a try disallowed for a forward pass from Flanagan after he danced around bewildered Bristol defenders Arscott and Hill.

Blair tied the game seven minutes later, yet Bristol established consistent field position - and their pressure told with a well-worked try.

Arscott received the ball in space, and his clever kick in field was merely flicked on by a retreating Robinson to Hill - who dived over between the posts.

Strange slotted the conversion, and the Blues had it all to do as Bristol's pack retained a vice-like grip on proceedings.

Cardiff were outgunned in key contact areas, yet the Blues stung their opponents by stealing an opportunist try during first-half injury time.

Bristol were anxious to preserve their 10-point advantage, but Flanagan's kick over the defence was caught by Robinson - and he easily touched down.

Blair's conversion made it 13-10 at the break, but Bristol - given their dominance up front - should have been clear on the scoreboard.

Bristol head coach Hill made an interval switch, sending on Samoan flanker Alfie To'oala for Joe El Abd.

Cardiff, though, drew level through another Blair penalty.

For the first time, Bristol showed signs of creaking - and prop Jason Hobson's needless backchat to Irish referee Peter Fitzgibbon helped Cardiff gain further ground.

Bristol had lost direction and a degree of composure, and Hill decided on two further changes as forwards Roy Winters and Dan Ward-Smith joined the action.

The visitors hardly helped themselves when prop Darren Crompton was sin-binned for a high tackle on Tom Shanklin that stopped the Wales centre in his tracks.

Bristol lost their way after Crompton exited, conceding scores to Molitika and Williams as they ended a disappointing contest well beaten.