Tries by Nic Rouse and Marland Yarde were not enough as two tries by Dean Mumm and Ben White and 19 points off the boot of Gareth Steenson saw the visitors prevail.
Brian Smith’s side were forced into a late change as they lost Topsy Ojo in the warm up with a suspected hip injury.
To add to their woes, Irish ill discipline was costing them dearly in the opening 10 minutes as Gareth Steenson kicked a long range penalty to give his side the early advantage.
Both sides were looking to play with width early on, with Ian Humphreys passing plenty of long passes to his outside backs enticing them onto the gain line.
Ian Humphreys booted his side’s first points on 19 minutes which their endeavour deserved. Unfortunately, trying to play too much was the Exiles downfall as the visitors forced them into mistakes and Gareth Steenson capitalised with two further penalty goals.
At 3-9 down the Exiles needed to reply and they duly did with the forward pack putting in the hard yards. After Halani Aulika was denied a try by the TMO, Irish regrouped and came again through their forward pack. After four phases, Nic Rouse was bundled over the try line aided by his prop forward, Matt Parr. Humphreys converted to put Irish in front for the first time in the match.
The Exiles lost exciting front row forward Halani Aulika, after he had superbly turned over the ball he fell awkwardly with a suspected ankle injury five minutes before the break. He was replaced by Leo Halavatau.
Errors scuppered Irish’s chances of adding to the score as it remained 10-9 at the half time interval.
Exeter started the second stanza the brighter side, utilising their forward power to bring Steenson a further opportunity to kick for goal. He made no mistake and put Exeter back in front.
Humphreys kicked his second penalty on 52 minutes after great lead up work from Alex Lewington put Irish in a promising position.
The penalty sparked a fantastic period for the Exiles. Bryn Evans intercepted the ball from the following re-start and galloped his way up field. The All Black was tackled just short of the line. After a quick clean by the supporting players the ball was spun wide to Ian Humphreys who sent the ball onto Alex Lewington. The full back made no mistake with the one on one and passed onto Marland Yarde who had his fourth try of the season. Humphreys conversion saw Irish pull out eight points ahead at 20-12.
Ian Humphreys added a further three points for Irish which Gareth Steenson quickly cancelled out with his fifth penalty of the afternoon with 20 minutes remaining.
This was the big turning point in the fixture. Irish lost a man to the sin bin and paid the ultimate price when Dean Mumm crossed for an Exeter score.
The visitors had the momentum with them and six minutes after the Mumm crossed, they were in for their second try. Ben White bundled his way over as the ball squirted out of the scrum. Steenson kicked the conversion to give his side a six point buffer which was enough to claim the victory.
Irish travel to The Rec next Saturday to take on Bath in Round four of the Aviva Premiership.
Score sequence (London Irish first): 0-3, 3-3, 3-6, 3-9, 10-9; 10-12, 13-12, 20-12; 23-12; 23-15, 23-22; 23-29
Scorers: London Irish; Penalties: Humphreys (19, 52, 56); Tries: Rouse (30), Yarde (53); Conversions: Humphreys (2); Exeter Chiefs: Penalties: Steenson (6, 22, 25, 48, 61); Tries: Mumm (67), White (73); Conversions: Steenson (2)
15. Alex Lewington; 14. Marland Yarde; 13.Fergus Mulchrone (rep: Sailosi Tagicakibau, 76); 12. Eamonn Sheridan; 11. Andrew Fenby; 10. Ian Humphreys (rep: Matt Parr, 69); 9. Tomás O’Leary (Captain) (rep: Darren Allinson, 74); 1. Matt Parr (rep: John Yapp, 59; rep: Shane Geraghty, 76); 2. David Paice (rep: Jimmy Stevens, 73); 3. Halani Aulika (rep: Leo Halavatau, 35); 4. Nic Rouse (rep: Ian Nimmo, 45-48); 5. Jebb Sinclair (rep: Ian Nimmo, 71); 6. Declan Danaher; 7. Bryn Evans; 8. Ofisa Treviranus
Replacements: 16. Jimmy Stevens; 17 John Yapp; 18. Leo Halavatau; 19.Ian Nimmo; 20. Gerard Ellis; 21. Sailosi Tagicakibau; 22. Shane Geraghty; 23. Darren Allinson
15. Phil Dollman; 14. Ian Whitten; 13. Jason Shoemark; 12. Sam Hill (rep: Matt Jess, 55); 11. Tom James; 10. Gareth Steenson; 9. Haydn Thomas (rep: Dave Lewis, 57); 1. Brett Sturgess (rep: Benn Moon, 54); 2. Jack Yeandle (rep: Chris Whitehead, 67); 3. Hoani Tui (rep: Carl Rimmer, 58); 4. Dean Mumm (Captain); 5. Damian Welch; 6. Ben White; 7. James Scaysbrook; 8. Tom Johnson
Replacements: 16. Chris Whitehead; 17. Ben Moon; 18. Carl Rimmer; 19. Tom Hayes; 20. Kai Horstmann; 21. Dave Lewis; 22. Henry Slade; 23. Matt Jess
Referee: Andrew Small