Irish could not have made a worse start when outside centre Tim Streather rounded off a slick Saracens back move to put his side ahead after just 50 seconds.

England fly half Owen Farrell added the extras and then slotted a penalty to put the visitors 10-0 ahead, but Irish fought back and flanker Blair Cowan crossed to reduce the arrears.

Saracens looked potent however, and following another Farrell penalty, scrum half Richard Wigglesworth scooted home from 20 yards out after spotting a gap at the base of a ruck. With the conversion knocked over, Sarries led 20-7 and a rout looked a possibility.

However the Exiles got themselves back into the game courtesy of a brilliant try from Lewington, who gathered a cross-kick by Kiwi fly half Chris Noakes and dotted down in the corner.

And the winger cut the gap to just one point after gathering Scott Steele's grubber kick and beating two men to grab a stunning second.

Another Farrell penalty saw Saracens to a 23-19 half time lead, but Geragthy cut the gap with a penalty at the start of the second period.

Lewington completed a magnificent hat trick shortly after, again gathering a Steele kick to scorch home from 40 metres out and put the Irish supporters in dreamland.

Alex Goode knocked over a penalty to make the score 29-26, and the full back then exchanged further three-pointers with Geragthy as the game continued at a breathless pace.

The pair then both missed two chances - Geragthy's from distance and Goode's more straightforward - as it appeared it may be Exiles' day.

But they conceded a penalty two minutes from time at the scrum - a problem all game - which Sarries bravely kicked to the corner.

And their faith was rewarded as Vunipola crashed over at the back of a powerful driving maul to give his side an enthralling win, while Irish were left with just two bonus points after a superb performance.

London Irish: Fenby, Lewington, Mulchrone, Geraghty, Short, Noakes, Steele; Court, Paice, Aulika, Skivington (c), Sinclair, Cowan, Treviranus, Narraway.

Subs: Ellis, Parr, Halavatau, Leo, Low, Guest, O'Leary, Sheridan.

Saracens: Goode, Ashton, Streather, Barritt (c), Wyles, Farrell, Wigglesworth; Gill, George, Longbottom, Hamilton, Smith, Joubert, Burger, Vunipola.

Subs: Spurling, Barrington, Johnston, Botha, Wray, de Kock, Hodgson, Taylor.

Referee: Lee Pearce

Attendance: 6.655.