But it is the Ospreys, the Blues’ fierce local rivals, who have most to celebrate. A victory away to bottom team Border Reivers tomorrow will give them the championship.

Leinster, for whom a bonus-point win would have made the Ospreys’ effort irrelevant, have only themselves to blame.

They had the lion’s share of possession and territory in the first half without turning it into points and then, as their dream slipped away, their play became ever more ragged.

The Blues, with an unbeaten home record to protect, left no doubt about their intentions, crossing for a superb try after just five minutes.

Following a driving line-out fly-half Nicky Robinson, with a point to prove after being omitted from the Welsh tour party for Australia, knifed between opposite number Felipe Contepomi and flanker Keith Gleeson and sent the supporting Robin Sowden-Taylor over.

Contepomi responded with a penalty but Leinster, desperate for tries, spurned further kicks at goal to go for position with only solid Blues defence – notably one tackle by Jamie Robinson on the burly Shane Horgan – keeping them at bay.

When the Irish province were awarded another penalty after Rob Kearney brilliantly reclaimed his own high kick, Contepomi opted to take the three points.

It was ironic therefore when the Blues, on a rare visit to the Leinster 22, chose to put a kickable penalty into touch and the pack carried hooker Gareth Williams over for a second touchdown.

And the Blues went further ahead early in the second period with an inch-perfect cross kick by Nicky Robinson being caught by Chris Czekaj, who drew the last defender to send fellow wing Rhys Williams in and Ben Blair converted.

A disastrous error by Horgan gifted the Blues a fourth try and a bonus point. The centre tried to chip Marc Stcherbina, but his kick was too low and the Australian centre grabbed it and strolled over for Robinson to add the extras.

Horgan quickly made up for his mistake, hacking the ball downfield for 50 yards and, once Rhys Williams had failed to clear, the big centre won the race to touch down.

Contepomi missed the conversion and his evening went from bad to worse when he was dispatched to the sin-bin after taking out Jamie Robinson in mid-air as the Blues man jumped to claim a high kick.

The visitors hurled the ball around in desperation but never looked like reducing the deficit.