Blues (10) 34
Martyn Williams claimed two of Cardiff Blues' four tries
Tries: Robinson, Molitika, M Williams 2.
Cons: Blair 4.
Pens: Blair 2.
Bristol (13) 18
Tries: Hill, Arscott.
Pens: Strange 2.
Cardiff Blues came from behind against a fierce Bristol effort to claim a bonus-point win in their Heineken Cup opener at the Arms Park.
The turning point, with the game locked at 13-13 midway in the second period, came when Bristol prop Darren Crompton was sin-binned for a high tackle.
Maama Molitika and Martyn Williams, with two, soon claimed Blues tries.
Bristol scored a late consolation try through Tom Arscott, adding to Dave Hill's first-half effort.
Blues were the first to cross the line when Tom James jinked his way through on five minutes, only for the wing to be called back for a forward pass earlier in the move.
Despite the home side applying most of the early pressure it was Bristol who took the lead when former Ebbw Vale and Newport fly-half Jason Strange stroked over a penalty against his countrymen.
Ben Blair replied in kind for the Blues, but they then were hit by a swift Bristol counter-attack after losing possession.
Shaun Perry spotted space on the right and fizzed a flat pass out to Arscott, who chipped ahead and showed great pace to challenge Blair for the bouncing ball.
Hill was in support to take the knock-back and saunter under the posts to give Strange a simple conversion.
The rest of the half belonged to the Guinness Premiership side as they pinned the Blues back in their own half.
Darren Crompton's sin-binning for this high tackle was a turning point
But the Welsh dug deep in defence and limited Bristol to one more Strange penalty.
Then, just before the half-time whistle, Blues lifted the siege and at last moved into the Bristol 22 to score their first try.
Young fly-half Dai Flanagan, only playing because of injuries to more senior 10s, produced a perfect chip for centre Jamie Robinson to gather in his stride and go under the posts.
Blair converted to ensure the home side trailed just 10-13 at the break.
Bristol had the chance to draw first blood after the restart but Strange hooked a relatively simple penalty kick.
That allowed Blair to bring the Blues level soon after with his own kick from in front of the posts.
On 59 minutes Bristol lost Crompton to the sin bin after the prop tackled Tom Shanklin high, although Blair was short with the resulting long-range penalty attempt.
But the man advantage soon told as the Blues backs broke through down the left.
Blair was hauled down just short but Molitika was on hand to place the ball over the line through a forest of legs and arms.
Four minutes later the Blues struck again down the left, with flanker Martyn Williams cutting back inside to score.
Blair converted both tries and suddenly, from struggling for much of the match, the Blues were in the clear with a 27-13 lead and nine minutes remaining to find a fourth try for a bonus point.
That soon arrived as a flowing move involving forwards and backs shredded the Bristol defence, allowing flanker Williams to power over for his second seven-pointer.
Arscott scored a late consolation for the visitors, but it was the Blues who left the Arms Park with five points to top Pool 3 alongside Stade Francais - who go to Bristol next week, while Harlequins host the Blues.
Blues director of rugby Dai Young:
"The try just before half-time was crucial for us, it settled us down a little bit.
"I always felt we would score the most tries and in the second half we had more intensity and broke away to claim some scores."
Bristol head coach Richard Hill:
"The players are angry with themselves for letting the lead slip, but there is a positive attitude that they can go and beat Stade Francais next Sunday.
"I think we have taken another step forward. The players will develop from this sort of game and we have got to try and get better in the competition.
"We got a bit tired in the second half with the number of tackles we had to make, but I thought the effort from the players was tremendous."
Blues: Ben Blair; Tom James, Jamie Robinson, Tom Shanklin, Gareth Thomas; Dai Flanagan, Jason Spice; John Yapp, Gareth Williams, Taufa'ao Filise, Deiniol Jones, Paul Tito, Maama Molitika, Martyn Williams, Xavier Rush (capt).
Replacements: Gethin Jenkins for Yapp (51), T Rhys Thomas for G. Williams (67), Robert Sidoli for Jones (75), Scott Morgan for Rees (78), Richie Rees for Spice (75), Tal Selley for J. Robinson (79), Rhys Williams.
Bristol: David Hill; Tom Arscott, Rob Higgitt, Sam Cox, Lee Robinson; Jason Strange, Shaun Perry; Darren Crompton, Mark Regan, Jason Hobson; Nathan Budgett, Sean Hohneck; Matt Salter (capt), Joe El Abd, Andrew Blowers.
Replacements: David Blaney for Regan (74), Alex Clarke for Ward-Smith (62), Roy Winters for Budgett (51), Alfie To'oala for El Abd (41), Dan Ward-Smith for Salter (51), Brian O'Riordan for Strange (78), Josh Taumalolo for Hill (67).
Referee: Peter Fitzgibbon (Ireland).