Dragons 17 (10)
London Irish fly-half Mike Catt tackles Richard Mustoe
Tries: Owen, S Jones
Cons: Sweeney (2)
London Irish 45 (31)
Tries: De Vedia (2), Catt, Armitage (2), Kennedy
Cons: Hewat (6)
London Irish blitzed the Dragons at Rodney Parade to record their second successive Pool One bonus-point win.
Tomas De Vedia (2), Mike Catt and Delon Armitage secured the crucial four tries inside half-an-hour, before the shell shocked home side got a Mike Owen try.
That was little comfort as Catt and Peter Richards ran the show, Peter Hewat kicking superbly for 15 points.
Nick Kennedy and Armitage crossed after the break, against a consolation Dragons score from hooker Steve Jones.
An excellent early break from Rhodri Gomer-Davies nearly put Luke Charteris in at the corner, and Ceri Sweeney hit the post with a penalty resulting from the home side's pressure.
But Exiles half-backs Richards and Catt quickly took control, Richards winning a penalty converted by Hewat after a cynical block from Sweeney.
Richards and Catt combined to deliver quick ball for the visitors' three-quarters, and with the Dragons defence stretched De Vedia went over in the corner for the opening try.
Richards took a quick tap penalty after a Dragons line-out mistake, feeding Armitage who chipped over the top.
That was a 20 minutes like I have never experienced before, we fell asleep and they gave us a lesson in finishing
Dragons coach Paul Turner
Wales full-back Kevin Morgan, making his return after a knee injury, made a hash of gathering the wickedly bouncing ball, De Vedia collecting for his second try.
The demoralised Dragons let Catt through for a walk-in try after a neat off-load from Tonga Lea'aetoa.
Sweeney eventually got the home side on the board with a 24th-minute penalty, but Catt inspired more fine Exiles three-quarter play and Armitage showed good strength to cross for the bonus-point try in the 29th minute.
The Dragons went back to basics, and a series of short-range forward drives ended with a try for the outstanding Owen, the lock reaching over the top of a pile-up on the Exiles' line.
But after the break another mistake from the Welsh side saw the lethal visitors profit, Sailosi Tagicakibau hacking on following a lost Dragons line-out.
You won't get conservatism with someone like Mike Catt
London Irish coach Toby Booth
The wing then combined with Seilala Mapausua to free supporting lock Kennedy, who romped in at the corner to crown a man-of-the-match performance.
Sweeney was held up on the London Irish line, but hooker Jones followed up for the Dragons' second try.
As the home side threw caution to the wind, the Exiles increased their misery when Armitage plucked off Andy Williams' pass for a simple interception try, ensuring their biggest ever Heineken Cup win and their first on the road in the tournament.
Dragons coach Paul Turner:
"That was a 20 minutes like I have never experienced before, we fell asleep and they gave us a lesson in finishing.
"I felt we had prepared well and targeted Peter Richards and Mike Catt - but we never laid a hand on them and their pack also did a number on us in that opening.
"I feel for my players, but this is Europe and when you make mistakes you get punished.
"It's not the end of the world. We're a small, tight-knit squad who are moving forward, but we got taught some lessons today."
London Irish coach Toby Booth:
"Mike Catt is expanding his coaching role with us, but I am sure as long as his body allows him to, Mike would want to play first and coach second.
"Having a midfield general like him around to take the pressure off is so important. He brings fantastic experience and leadership qualities that are vital in pressurised environments.
"We believe that attack is our best form of defence, and you won't get conservatism with someone like Mike Catt.
"A bonus point win here was probably beyond our expectations. Our defence has to take a lot of credit for forcing turnovers, and we capitalised on that.
"There is still a lot to do, our aim is to reach the quarter-finals, it is one of our internal goals, and it is something that we haven't achieved before."
Dragons: Morgan, Wyatt, Davies, Smith, Mustoe, Sweeney, W. Evans, Black, S. Jones, R. Thomas, Charteris, Owen, Ringer, Parks, Charvis.
Replacements: Emerick for Wyatt (56), A. Thomas for Sweeney (69), A. Williams for W. Evans (59), Gustafson for Black (69), Daly for S. Jones (69), Hall for Owen (74), Bearman for Parks (59).
London Irish: Hewat, De Vedia, D. Armitage, Mapusua, Tagicakibau, Catt, Richards, D. Murphy, Paice, Lea'aetoa, Kennedy, Casey, Roche, Danaher, Leguizamon.
Replacements: Ojo for Hewat (80), Hodgson for Catt (55), S. Armitage for Richards (69), Coetzee for Paice (69), Skuse for Lea'aetoa (49), Hudson for Kennedy (79), Thorpe for Leguizamon (63).
Referee: Christophe Berdos (France)