Cardiff Blues blazed into the Heineken Cup quarter-finals after recording a remarkable victory at Kingsholm.

The Welsh side played for 53 minutes of a fierce encounter with 14 men after their international wing Tom James was sent off.

But Gloucester could not make their advantage count as substitute lock Bradley Davies powered over for the winning try four minutes from time.

Full-back Leigh Halfpenny kicked three penalties and a conversion and Gloucester had to settle for a losing bonus point despite leading 12-6 through four penalties by Olly Barkley.

The Blues, unbeaten Pool Six leaders, marched on following a fifth successive win.

And if they collect an anticipated bonus point success at home to Italian whipping boys Calvisano next Friday, they will progress as top seeds.

Gloucester's quarter-final progress is now in the lap of the gods.

They effectively need a bonus-point win against 2006 Heineken Cup runners-up Biarritz in France, but will still have to rely on other results going their way.

The most likely scenario is a damaging pool stage exit, yet they could have few complaints after the Blues outmuscled them through a performance which bristled with passion and endeavour.

James was dismissed in the 27th minute for butting Gloucester hooker Olivier Azam, leaving his team a mountain to climb and potentially dashing his hopes of challenging for a place in Wales' RBS 6 Nations squad, which is announced tomorrow.

Barkley's penalties looked to have tilted the balance in Gloucester's favour, his efforts coming just four days after he was dropped from the elite England squad by manager Martin Johnson.

But the Blues never threw in the towel during an attritional contest dominated by the packs on a heavy surface.

Gloucester suffered a double injury blow as England backs Mike Tindall (leg) and Olly Morgan (finger) were both ruled out, meaning a major back division reshuffle.

Willie Walker replaced Morgan at full-back, while Matthew Watkins moved into midfield as Tindall's deputy and James Simpson-Daniel lined up on the wing for a first start since Gloucester lost to Cardiff three months ago.

Number eight Luke Narraway took over from Tindall as captain, but the Blues had few problems in comparison, fielding five of the Wales side which beat Australia in November.

Gloucester bossed the initial exchanges and took a seventh-minute lead when Barkley rifled over a 51-metre penalty.

Halfpenny hauled the Blues level 10 minutes later, but the visitors then put themselves in self-inflicted trouble.

Barkley's second penalty edged Gloucester back in front before a skirmish between James and Azam left referee Alan Lewis with little option other than to send James off.

The players squared up to each other and, after an initial pushing match, James butted Azam in full view of Lewis.

It meant the visitors having to play more than 50 minutes with 14 men, and when Barkley completed his penalty hat-trick shortly afterwards, alarm bells started ringing at 9-3 adrift.

The visitors needed to regroup during half-time and their response must have thrilled head coach David Young.

Halfpenny's second successful penalty cut the gap to three points, and despite Blues' numerical disadvantage, they kept creating chances.

Halfpenny though, drifted a penalty wide that would have levelled the score, then scrum-half Jason Spice was agonisingly denied a try.

Hooker Gareth Williams' initial surge caused damage to Gloucester's defence, but despite Spice crossing the line, video referee Marshall Kilgore ruled he had not grounded the ball.

It was a blow for the Blues and Gloucester responded by relieving mounting pressure on their 22, allowing Barkley a fourth penalty that made it 12-6 with 20 minutes left.

Halfpenny's second miss provided a let-off for Gloucester, before he regained his nerve to complete a hat-trick nine minutes from time.

And the closing stages belonged to try hero Davies and the Blues, who are now the only team of 24 in this season's Heineken Cup still boasting a 100% record.