London Welsh captain Tom May and Irish replacement Dan Leo were both sent off after 34 minutes as Welsh went down to their 11th league defeat of the season.
May's action was similar to that of Northampton's Dylan Hartley last week as the skipper lashed out with a swinging elbow and though Leo initially appeared to be defending himself, having grappled May to the floor he punched the opposition centre and both earned their red card.
It was a close game until the sendings-off but after the interval, the home pack dominated their opponents to secure a 24-9 victory.
In a game of poor quality, Alex Lewington, Geoff Cross and Tom Court scored tries for the Irish with Tom Homer converting all three and kicking a penalty. Three penalties from Will Robinson were Welsh's sole response.
Both sides made sweeping changes following heavy defeats last weekend. Irish made five, with lock Nic Rouse returning after injury and Shane Geraghty switching to centre to accommodate Chris Noakes at fly-half. Welsh changed seven, with Nick Scott included on the wing and Dean Schofield in the second row.
Irish had the better of a dreary opening and should have taken the lead but surprisingly Homer missed with a straightforward penalty attempt. Minutes later, the full back was given another chance but again failed, this time from the halfway line.
After 15 minutes, Welsh made the first trip into the opposition half and they had an opportunity to open the scoring and Robinson made no mistake with an excellent kick from 50 metres out.
Irish declined a kickable penalty in favour of an attacking line-out but carelessness saw them lose possession as they attempted a driving maul.
Irish dominated the first quarter but they trailed 3-0 at the end of it - but when Piri Weepu was penalised for a high tackle, Homer's penalty put the home side level.
After 29 minutes, Irish scored the first try. A chip ahead by Geraghty should have been dealt by the visitors' defence but a favourable bounce saw Fergus Mulchrone collect to send Lewington in for the try which Homer converted.
Lock Leo had temporarily replaced Kieran Low just before Lewington's try but after 34 minutes he was sent off. At a maul near half-way Leo appeared to be obstructing May, who lashed out with a swinging elbow catching Leo in the face.
The replacement retaliated by wrestling May to the floor before punching him and after consultation with the TMO, referee Greg Garner gave both players their marching orders.
Robinson kicked his second penalty for Welsh but the hosts looked to have extended their lead when another chip from Geraghty was pounced upon by Ojo for the wing to touch down. However the replay showed Ojo to be just in front of the kicker so the TMO ruled no try leaving Irish with a 10-6 lead at the interval.
Irish took off Noakes at half-time, replacing him with flanker Conor Gilsenan to strengthen their forward unit as Geraghty switched from centre to fly-half.
This paid dividends as the Irish pack continued to be in control and were rewarded when prop Cross forced his way over from close range for a try which Homer converted.
Robinson kicked his third penalty to make it 17-9 at the end of the third quarter but Irish clinched victory when Court finished off a line-out drive for their third try which Homer again converted to ensure Welsh remained winless.