Former Munster and Ireland scrum-half Tomas O'Leary could face a hefty ban after being sent off for stamping in London Irish's 23-20 Premiership victory over Wasps at Adams Park.

The second-half incident, where O'Leary put his foot down on James Haskell's head, marred an otherwise tough local derby between the two Thames Valley-based Londoners.

English Rugby Football Union disciplinary rules indicate a ban of two to nine or more weeks for stamping on an opponent but trampling on the head is likely to be at the higher end of the scale.

There were some good scores in the game as Irish went ahead with tries from out-half Ian Humphreys and hooker David Paice against one touchdown for wing James Short during the first-half.

All Wasps other points came via five penalties from fly-half Joe Carlisle, while full-back James O'Connor landed two penalties and two conversions and centre Shane Geraghty kicked a late drop-goal for the Exiles.

Wasps were aiming for their third victory over Irish in all competitions season but it was the men from the Madejski Stadium who stung the home side early in the first-half.

Full-back Elliot Daly tried to clear a ball from his own line but lock Nic Rouse was up on the clearance attempt in a flash. He charged it down and, as the fall ran free, Humphreys picked up and drove over from a few yards.

Irish had the bit between their teeth, hoping to add another big capital city scalp to that of leaders Saracens last week, whom they shocked 22-13 at Allianz Park.

And, when O'Connor added a 28 metre penalty to the conversion of Humphreys' touchdown on seven minutes, Wasps were already looking shaky.

However, Carlisle's kick of the game, a penalty from 40 metres when Irish strayed offside at a ruck, steadied the home ship for a moment.

Irish, though, turned the screw again. Prop Matt Parr drove over from a metre but his try attempt was ruled out by TV match official Rowan Kitt.

It was just a short wait, however, for their second when an attacking scrum saw number eight Ofisa Treviranus pick-up and drive towards the corner. Two plays on the Wasps line later, Paice grabbed the touchdown that, with O'Connor's second conversion of the match, put the visitors 14 points ahead.

Wasps needed something on the scoreboard quickly and they found it when centre Andrea Masi put a lovely grubber kick past the Irish defensive line on the left for Short to just get the slightest downward pressure for the score.

Captain Chris Bell roused his side and forced Irish onto the back foot in their own 22 as the home team looked to reduce the arrears. They should have done so as well but Masi, with just a couple of metres to the line, dropped a simple pass.

That finished a rousing half and Wasps continued their pressure into the second period, with Carlisle punishing Irish for a line-out offence for three more points from thirty metres.

But, with 48 minutes gone, O'Leary had his moment of madness. The ruck he stood behind was as ordinary as any in the game but he put his foot down heavily on Haskell's head and, after reviewing it, ref Tim Wigglesworth went straight to his pocket for the red card.

The mistakes came from Irish and their lead eroded as Carlisle kicked three more penalties against one from O'Connor to level the match at 20-20 with ten minutes to go.

Then Irish delivered a killer blow as they pressurised Wasps in the 22 and, Geraghty, stood behind the posts, launched over a twenty metre drop goal as the home side were sunk.