Full-time: Gloucester 12 Cardiff Blues 16: Gloucester's Heineken Cup hopes hang by the thinnest of threads following an agonising Pool Six defeat against 14-man Cardiff.

Bradley Davies' late try, which was converted by Leigh Halfpenny, turned a 12-9 deficit into a 16-12 lead with three minutes to play after Cardiff had played for the best part of an hour with 14 men after Tom James' red card.

Gloucester now trail the Blues by seven points – and must win well in Biarritz on Friday, as well as seeing other results go their way, to have any chance of reaching the last eight.

Olly Barkley's four penalties looked like being enough to take Gloucester to within a point of the pool leaders – only for Davies' late intervention to give the dogged Blues a deserved victory.

The game was finely balanced at 6-3 when winger James inexplicably butted Olivier Azam and was shown a straight red card.

Gloucester, who had Mike Tindall (dead leg) and Olly Morgan (dislocated finger) ruled out 24 hours before kick-off, took an early lead when Barkley landed a 53-metre penalty after Cardiff were penalised at a scrum.

The hosts threatened to add to their early score but were unable to find a way through a resilient Blues defence before the Welsh side levelled with a Halfpenny penalty following an offside.

Barkley made it 6-3 when Cardiff killed the ball – and then came the drama which saw James sent off just seconds after a promising Blues attack had faded just metres from the line.

Cardiff went over the top at a ruck, allowing Barkley to make it 9-3, and the centre hit the bar with another penalty shortly before the break as Gloucester began to assume control of the game.

They started the second period on the back foot, though, with Cardiff cutting the Gloucester lead to three points through another Halfpenny penalty after the full-back had been shoved by Marco Bortolami.

Halfpenny then failed with another penalty attempt, before the television official denied the Blues a try – even though referee Alan Lewis appeared to signal the score was good.

Ryan Lamb kicked to touch but the ball had been passed back into the 22 so Cardiff secured line-out ball deep in home territory. They moved the ball quickly and cleverly through Andy Powell and Gareth Williams, before Jason Spice arrived right on the line.

The scrum-half thought he had scored, but the television official spotted that Alex Brown had held him up.

Gloucester managed to break out of their own half midway through the second half – and were unfortunate that Willie Walker knocked on after they had snatched possession when Cardiff overthrew a line-out.

Barkley relieved some of the pressure on Gloucester with his fourth successful penalty of the afternoon to make it 12-6 with 20 minutes to play, before Halfpenny failed with a 40-metre penalty.

But the 20-year-old found his range to cause Gloucester jitters when acting skipper Luke Narraway was penalised on the floor, landing the penalty to make it 12-9 with nine minutes left on the clock.

And with three minutes to play, Cardiff were 16-12 in front. Walker's kick to touch under pressure was poor, offering the visitors a line-out in the home 22.

They secured the ball, then excellently kept possession from left wing to right, with Taufa'ao Filise and Maama Molitika battering a route for replacement Davies to power his way over the line. Halfpenny converted from close to the touchline to give the Blues a four-point lead.

Gloucester: W Walker; I Balshaw, M Watkins (A Allen 65), O Barkley, J Simpson-Daniel; R Lamb, G Cooper (D Lewis 65); A Dickinson (N Wood 58), O Azam (A Titterrell 73), C Nieto, M Bortolami (W James 48), A Brown, A Strokosch, A Satala, L Narraway (capt). Reps not used: A Eustace, M Foster.

Scorers: Pens – Barkley (4).

Cardiff Blues: L Halfpenny; G Thomas, T Shanklin, J Roberts, T James; N Robinson, J Spice; G Jenkins, G Williams (T R Thomas 73), G Powell (T Filise 62), D Jones (B Davies 65), S Morgan, M Molitika, M Williams (capt), A Powell (X Rush 69). Reps not used: D Allinson, C Sweeney, J Robinson.

Scorers: Try – Davies. Con – Halfpenny. Pens – Halfpenny (3).

Sent off: James (30, striking opponent with head).

Referee: A Lewis (Ireland). Att: 14,916.