Only seven points separated the sides at half time, thanks to tries from Aled Summerhill and Seb Davies.
However, the Exiles sealed a bonus point shortly after half time, as Ofisa Treviranus went over for his second score, and went on to open a comfortable lead over the hosts.
Corey Domachowski crossed the whitewash for a consolation score late on, but danger-man, Joe Cokanasiga got his name on the scoresheet in the final play of the game.
The visitors were dealt an early blow as captain Mike Coman was forced off the field with only two minutes on the clock.
The Exiles looked to get in-form wing, Cokanasiga, into the game as much as possible in the opening stages, and he proved to be a handful for the Cardiff Blues defence with his combination of pace and power.
However, it was the man on the opposite end of the pitch, Alex Lewington, who opened the scoring for the visitors.
Theo Brophy Clews spotted the Saracens-bound man in acres of space out on the left, and a driven kick was enough to send the wing over the whitewash. James Marshall made no mistakes with the conversion.
Richard Hodges’ side bounced back in stunning fashion to bring the scores level, as a long kick downfield by Clews allowed Rhun Williams to run back and make half a break down the centre, setting up a promising attacking platform for the Blues.
The ball was shipped wide to Garyn Smith, who poked the ball past the Irish defence, picking out debutant Ryan Edwards. Full back Marshall was drawn towards the wing, but he found support on his inside from Summerhill, who showed a turn of pace to go over for the score.
Steven Shingler converted, but the home side’s lead would be short-lived. London Irish quickly found themselves going through the phases at the opposite end of the pitch, with number eight, Treviranus, eventually crashing over from close range.
London Irish had a golden opportunity to add a third after 30 minutes, as a penalty resulted in a line-out on the Cardiff Blues five-meter line. The pack attempted the drive, but James Down proved a handful the maul and forcing a turnover.
A speculative kick from Shingler cruelly bounced away from Sumerhill, allowing Marshall to run back into the Blues’ 22.
The full back found Springbok Pieter van Zyl in support, who offloaded to Clews. The outside half looked to put the decisive pass to Max Northcote-Green, who knocked it on with the try-line begging.
The missed opportunity proved costly for Nick Kennedy’s side, as the home side came back flying. Smith broke down the centre and found Davies on his outside.
The number eight galloped downfield, and despite being shepherd by Cokanasiga, a powerful hand-off was enough to keep the wing away, paving the way for a touch down out wide.
However, the visitors did head into the interval with the lead, as Arno Botha powered over under the sticks, following a patient set in attack.
The Exiles opened up breathing space on the scoreboard within five minutes of the second half. Williams showed courage to pounce on a kick behind the Cardiff Blues defence, denying Botha his second of the evening.
However, the back row managed to force the young full-back behind his own try-line, and Treviranus was over for his second from the resulting five-meter scrum, sealing the bonus point for his side.
The home side put a period of sustained pressure on the visiting defence, as they looked to fight their way back, but Botha intercepted and looked clear for a score.
Williams showed impressive pace to catch up with the blindside flanker, but Tom Fowlie was in support to run in unopposed for London Irish’s fifth try of the game, putting the result beyond doubt.
Replacement prop Corey Domachowski powered his way over from five-meters out for a consolation score, but a Johnny Williams break released Cokanasiga through for another try in the final play of the game.