Wasps (23) 33
Try: Penalty, Varndell, Ward-Smith, Waldouck Cons: Walder, Cipriani Pens: Walder 2, Cipriani
London Irish (10) 22
Tries: Mapusua, S Armitage, Tideswell Cons: Lamb, Homer Pens: Lamb
Tom Varndell was one of four try scorers for Wasps at Adams Park
Wasps overtook London Irish to move fourth in the Premiership following an entertaining win over their rivals.
A fourth-minute penalty try and two penalties saw Wasps take a 13-0 lead.
Irish hit back with a Seilala Mapusua score, but the hosts took a 23-10 half-time lead through well-worked tries from Tom Varndell and Dan Ward-Smith.
Dominic Waldouck finished off a superb move in the 50th minute but Steffon Armitage and James Tideswell tries set up a tense final 10 minutes.
But fly-half Danny Cipriani, on as a first-half replacement for Dave Walder, secured the victory five minutes from time with a simple penalty after London Irish full-back Peter Hewat was pinged for a high tackle on Ben Jacobs.
Although Wasps have a one-point advantage over Irish in fourth place, Toby Booth's side still have a game in hand over their Wycombe-based rivals.
The hosts made a late team change before kick-off when Cipriani was replaced by Walder at 10, with the England international dropping to the bench.
And it was Walder's kick that created the first score of the match when Steffon Armitage was penalised for tackling the chasing David Lemi without the ball when the winger looked set to touch down.
Worse was to follow for the visitors as referee Rob Debney sent flanker Armitage to the sin-bin, with Walder adding the extras from in front of the posts.
The hosts made the most of their numerical advantage as fly-half Walder added two penalty kicks to extend the lead to 13-0 with Irish in disarray.
Despite their dominance, Wasps conceded a try in the 19th minute when their disorganised line-out allowed Mapusua to barge through from close range, with Ryan Lamb adding the extras.
The Exiles fly-half reduced the deficit to three points with a 25th-minute penalty, but Wasps hit back two minutes later when centre Waldouck's superb line break and chip was neatly gathered by winger Tom Varndell, who outpaced his equally fleet-footed counterpart Delon Armitage to score in the corner.
However, the home side were dealt a setback when the influential Walder was replaced on the half hour because of injury with Cipriani, named on the bench because of an ankle knock sustained in training on Friday, taking over the play-making duties.
And Ward-Smith extended the lead to 13 points just before the interval when he slid over in the right corner following quick passes from scrum-half Joe Simpson and Mark van Gisbergen.
Wasps extended their lead to 30-10 in the 50th minute when they capitalised on an Irish knock-on, with Cipriani bursting through the line with scintillating pace before feeding the perfect inside pace for Waldouck to touch down unopposed under the posts for a simple conversion.
Irish again displayed their obdurate mettle as they responded through their forwards, this time when Steffon Armitage, assisted by the considerable muscle of Chris Hala'Ufia, bundled over from close range, although Lamb skewed his conversion attempt.
And replacement prop Tideswell set up an enthralling final 10 minutes when he applied the necessary downward pressure on a loose ball after Warren Fury's box-kick at the base of a ruck inside Wasps' 22m line had been charged down, with Tom Homer adding the two points at 30-22.
But Cipriani's kick five minutes from time eased the nerves of the home crowd.
Wasps director Tony Hanks:
"It is knockout rugby from now on and if we'd been offered a five-point haul from a win over Irish we'd have bitten your hand off.
"Our scrum was effective. That's why we brought in former England prop Trevor Woodman to work with the scrum.
"He's been patient and it's a real credit to him and to the forwards because to be criticised publicly the way we were earlier in the year, then to come back as we have, that's tremendous.
"Danny Cipriani took a knock on the ankle early in the week and we decided that the team who trained together in our last session was the one we should begin with and it paid off."
London Irish head coach Toby Booth:
"I am disappointed with some inconsistency in the official's decisions.
"We have a penalty try against us after only three minutes but then we have an attack in front of the posts, they deliberately knock-on and the referee sends their guy to the bin but only gives us a penalty. That should also have been a penalty try.
"However, I was disappointed with the first 20 minutes because we did things I thought we'd got away from. The players knew that as well.
"We just did some things out there that we need to eliminate from our game, unforced errors in some cases. We had to recover from a difficult start, but we showed enough to suggest that we can still finish in the top four."
Wasps: Van Gisbergen, Varndell, Waldouck, Kefu, Lemi, Walder, Simpson, Payne, Webber, Broster, Ward-Smith, Skivington, Worsley, Rees, Hart, Fury.
Replacements: Jacobs for Kefu (50), Cipriani for Walder (34), Fury for Simpson (41), Lindsay for Webber (80), Taulafo for Broster (61), Betsen for Rees (50), Sackey for Fury (71).
Not Used: Baker.
Sin-bin: Kefu (25).
London Irish: Hewat, Rudd, Seveali'i, Mapusua, D. Armitage, Lamb, Hodgson, Murphy, Buckland, Rautenbach, Roche, Casey, Stowers, S. Armitage, Hala'ufia.
Replacements: Homer for Mapusua (50), Malone for Lamb (67), Corbisiero for Murphy (50), Coetzee for Buckland (68), Tideswell for Rautenbach (68), Garvey for Casey (64), Gibson for Stowers (47).
Not Used: Catt.
Sin-bin: S. Armitage (4).
Ref: R Debeny (England).