Alex Lewington crossed for a hatrick of tries on his 23rd birthday but it was not enough for the win as Saracens spoilt the party with a try in the last minute to snatch victory.
The visitors turned down a shot at goal with time almost up and opted instead for a kick to the corner. The call from captain, Brad Barritt, was rewarded when Billy Vunipola was bundled over for the winning score.
The Exiles managed to come away with two bonus points and plenty of positives ahead of next weekend's fixture away at Leicester.
Saracens opened the scoring only three minutes into the match and it was the side from North London at their ruthless best. Irish missed ouch when exiting from inside their own 22 and lacked organisation in their defensive line. The visitors took full advantage with Alex Goode making the initial break, passing to Owen Farrell who sent a wide pass to former Nottingham centre, Tim Streather, who crossed in the corner. Farrell added the conversion from out wide to make it 7-0.
Farrell kicked his first penalty on nine minutes before Irish crossed for their first try. Shane Geraghty ignited the attack with a chip kick over the top which was gathered by Fergus Mulchrone with the centre quickly offloading to Scott Steele who sprinted for the try line. The scrum half was dragged down just short of the line with Irish support enabling them to retain possession. The Exiles showed composure and when the ball was recycled Shane Geraghty passed a flat ball across two Saracens defenders allowing Blair Cowan to run through the gap that was created and score in the corner. Geraghty added the difficult conversion to bring Irish back into the match at 7-10.
The visitors added a second penalty goal through Farrell before Richard Wigglesworth raced over for his side's second try. Saracens exploited a poor Irish kick chase and created the overlap with Chris Wyles running up the left hand flank. The American was tackled on the 22, but with support available, the ball was quickly available and the scrum half scooted down the short side to score in the corner.
Trailing by 13 points an Irish response was required, and it came with two tries to winger Alex Lewington, with both being created by kicks. Chris Noakes was instrumental and his cross field kick saw the winger challenging for the ball against Saracens prop Kieran Longbottom. It was no contest and after gathering he stepped inside the attempted tackle and dived over for the try.
Lewington had his second four minutes after, with smart thinking by Scott Steele. Referee, Luke Pearce, was playing advantage for a ruck infringement so the Scot put boot to ball and kicked along the ground for Lewington to claim, step inside the defence and race over for his second try. Geraghty's conversion drifted just wide but his side were now back in the contest at 19-20.
Owen Farrell kicked his third penalty three minutes before the break to make it London Irish 19 Saracens 23 at half time.
Shane Geraghty made it a one point game with his first penalty of the match on 41 minutes before Lewington had his hatrick moments later and his combination with Steele again coming to the fore. Narraway passed to Steele from the back of a scrum and his well weighted kick was again gathered by Lewington, who still had plenty to do, but he evaded one tackler and sprinted away from another to score his third. Geraghty's conversion put Irish in front for the first time in the game at 29-23.
Alex Goode took on the kicking responsibilities for Saracens with two penalties inside six minutes to draw his side level. Shane Geraghty put Irish back in front with a 51 metre effort to make it 32-29 with 16 minutes left on the clock.
Saracens had one last chance having won a penalty in the final minute. Turning down the option of taking the points Brad Barritt opted for the corner as the visitors went for the win. A solid catch supplied the foundations for a powerful rolling maul and despite good defensive work from the Irish pack, Saracens trundled their way over with Billy Vunipola the man to touch the ball down and break Irish hearts. Hodgson stepped up for the conversion to add the extras, leaving a final score of 32 - 36.
Irish will now prepare for round four of the Aviva Premiership and a visit to Welford Road to face Leicester Tigers.
Post-match Brian Smith was pleased with the performance but disappointed to not win the contest stating, "the guys gave it everything today and to come up sort at the death is disappointing.
"That last 25 seconds doesn't define our performance and there are many positives to take into our match next week against Leicester Tigers."
Score sequence (London Irish first): 0-7, 0-10, 7-10, 7-13, 7-20, 14-20, 19-20, 19-23, 22-23, 29-23, 29-26, 29-29, 32-29, 32-36
Scorers: Saracens: Tries: Streather (2), Wigglesworth (23), Vunipola (79); Conversions: Farrell (2), Hodgson; Penalties: Farrell (9, 14, 37), Goode (50, 56); London Irish: Tries: Cowan (12), Lewington (30, 34, 45); Conversions: Geraghty (3); Penalties: Geraghty (41, 63)
15. Andrew Fenby; 14. Aex Lewington; 13. Fergus Mulchrone; 12. Shane Geraghty; 11. James Short; 10. Chris Noakes; 9. Scott Steele (rep: Tomas O'Leary, 53); 1. Tom Court; 2. David Paice; 3. Halani Aulika (rep: Leo Halavatau, 50); 4. George Skivington (Captain); 5. Jebb Sinclair (rep: Dan Leo, 53); 6. Blair Cowan; 7. Ofisa Treviranus (rep: kieran Low, 33); 8. Luke Narraway (rep: Tom Guest, 50)
Replacements: 16. Gerard Ellis; 17. Matt Parr 18. Leo Halavatau; 19. Dan Leo; 20. kieran Low; 21. Tom Guest; 22. Tomas O'Leary; 23. Eamonn Sheridan
Saracens15. Alex Goode; 14. Chris Ashton; 13. Tim Streather (rep: Duncan Taylor, 56); 12. Brad Barritt (Captain); 11. Chris Wyles; 10. Owen Farrell; (rep: Charlie Hodgson, 70) 9. Richard Wigglesworth (rep: Neil de Kock, 56); 1. Rhys Gill; (rep: Richard Barrington, 50) 2. Jamie George; 3. Kieran Longbottom (rep: james Johnston, 50); 4. Haydn Smith; 5. Jim Hamilton (rep: Mouritz botha, 50); 6. Ernst Joubert (rep: Jackson Wray, 56); 7. Jacques burger; (rep: Jackson Wray, 44-50) 8. Billy Vunipola
Replacements: 16. Scott Spurling; 17. Richard Barrington; 18. James Johnston; 19. Mouritz Botha; 20. Jackson Wray; 21. Neil de Kock; 22. Charlie Hodgson; 23. Duncan Taylor
Referee: Luke Pearce