London Irish (16) 32
Thompstone, penalty Cons:
Homer 2 Pens:
Northampton (15) 27
Reihana, Wilson Con:
Everitt, Reihana 4
Adam Thompstone scored a fine first try for the hosts on Sunday
London Irish ensured the party continued following Ireland's historic Grand Slam as they edged a see-saw Premiership game against Northampton.
Bruce Reihana and Roger Wilson helped Saints into the lead, despite Adam Thompstone's try for Irish.
They took the lead at the break thanks to Tom Homer's boot but three Reihana penalties restored Saints' lead.
Homer, just 18, then landed three more penalties of his own and the Exiles wrapped up victory with a penalty try.
The win cements the Exiles' place in the play-off positions, while a late Reihana penalty gave the visitors a losing bonus point.
London Irish were hosting their annual St Patrick's weekend game and there were more than 21,000 fans at the Madejski Stadium.
Many of them were already in party mood following Ireland's first Grand Slam in 61 years the day before but the Saints were determined to spoil the party and they took the lead with a marvellous try from deep inside their own 22.
Ben Foden, ignored by England but tipped as a possible Lions tourist, fielded a massive Mike Catt kick and characteristically spied the chance to counter.
He fed Reihana and three phases later the former All Black cut inside the cover defence to score, with Barry Everitt adding the conversion.
The visitors then lost promising second row Courtney Lawes to the sin-bin for sealing off the ball at a ruck just a couple of yards from the Saints line.
Despite taking a series of quick penalties the hosts were unable to score but they were soon on the board as Thompstone crashed over Foden to finish off a sweeping attack.
Homer landed a nerveless conversion from wide out and added a penalty as the Exiles scored 10 points in Lawes' absence.
A penalty apiece for Homer and Everitt made it 13-10 to the hosts and although Wilson crashed over to put the visitors back in front, a long-range Homer penalty gave Irish the half-time lead.
But the hosts lost open-side flanker Steffon Armitage, who was lively in all phases, to the sin-bin early in the second half and Northampton regained the advantage.
Reihana thumped over three penalties to put them eight points ahead but the hosts were determined not to let Irish rugby down on such a glorious weekend and hit back with venom.
They mounted a series of assaults and although Northampton kept their line intact, Homer kicked three penalties of his own to restore the one-point lead.
A final assault saw them awarded a penalty try after they splintered the Northampton scrum before Reihana kicked a last-gasp penalty to ensure Saints did not go home empty-handed.
London Irish coach Toby Booth on full-back Tom Homer:
"He does that week-in week-out in training. He is a metronomic kicker and is a natural at it.
"He's a great striker of the ball and therefore it goes absolutely straight.
"He has forgotten he is only 18 years old and he has kicked us to victory before a large crowd."
Northampton coach Jim Mallinder:
"At 60 minutes the game was ours for the taking and I am very disappointed that we didn't close it out.
"The decision-making in the last 20 minutes was not accurate enough and there were too many basic errors.
"We forced ball when we didn't have to and we should have kicked to the corners but we got needlessly turned over on a number of occasions."
Homer; Thompstone, Seveali'i, Mapusua, Tagicakibau; Catt, Hodgson; Dermody, Coetzee, Skuse, Hudson, Johnson, Danaher, S Armitage, Hala'ufia.
Richards for Seveali'i (59), Paice for Coetzee (50), Lea'aetoa for Skuse (57), Roche for Johnson (55), Thorpe for Hala'ufia (56).
Not Used: Fisher, Hickey.
S Armitage (46), Richards (79)
Foden; Reihana, Ansbro, Downey, Lamont; Everitt, Dickson; Tonga'uiha, Sharman, Stewart, Lawes, Kruger, Easter, Best, Wilson.
Mayor for Downey (74), Myler for Everitt (55), J Gray for Sharman (76), Hopley for Lawes (77), Rae for Easter (56).
Not Used: Smith, Dickens.