DAN Biggar picked himself up to kick a match-winning penalty to keep unbeaten Northampton on track in a tense finish at Franklin's Gardens.
The Wales fly-half endured a bruising but triumphant afternoon on his return to duty after the Lions tour.
Just before his crucial penalty in the 74th minute, Biggar needed treatment on a neck injury after he had been hurt in a tackle.
To the delight of the Saints support, he brushed himself down to finish off Irish thanks to a third penalty goal in a match return of 13 points.
The late kick came after Irish looked to have stolen a rain-soaked game thanks to a dominant lineout after overcoming a 17-0 deficit.
Irish's forward power brought two tries and some slick work in the 64th minute put full-back Tom Parton scampering through for a third.
Paddy Jackson, who converted both tries, then saw a dropped goal chance in the last seconds float wide having been partly put off by that man Biggar.
Even then the Northampton fans had to wait for the victory to be confirmed as referee Tom Foley called for a video check on a tackle by Courtney Lawes in the lead up to Jackson's dropped goal attempt. Foley, on his 100th Premiership appearance, ruled Lawes' intervention to be legal on a busy afternoon in which he blew up for 31 penalties in a match which also produced 37 lineouts.
Irish had used their forward drive to cut away at Northampton's bright start which had brought a 17-0 lead thanks to tries from backs Tom Collins and Matt Proctor.
The visitors twice engineered tries from forward drives in a dominant middle period.
However, Irish were let down by their discipline especially No.8 Albert Tuisue who twice gave away penalties in the second half which Biggar slotted.
The second half had descended into a stop-start affair and contrasted to a fast start by Northampton.
For 20 minutes, the Saints played with a fizz and buzz generated by the confidence of that win at Exeter last week.
Irish struggled to cope and were relieved that Northampton managed only two tries in building their early lead.
Scrum-half Alex Mitchell made the break which led to the first try for wing Tom Collins following Biggar's opening penalty in the second minute. Collins took his chance six minutes later by accepting Fraser Dingwall's pass after Mitchell had broken through.
Northampton's second try was a smart score and again rewarded pressure off a midfield lineout.
This time full-back George Furbank spotted space behind the defending line to slot a neat kick into the path of the on-running Proctor.
Biggar converted both tries to give Northampton that 17-0 lead.
Irish did far better as the half closed forcing a succession of lineouts which eventually yielded a try for hooker Agustin Creevy which Jackson converted.
Irish continued the tactic of using a dominant lineout in the second half to earn a penalty try as Northampton had two players sin binned – Api Ratuniyarawa and Paul Hill – in quick succession.
A second penalty from Biggar eased Northampton's nerves at 20-14 but Irish slipped away for a third try when Parton escaped on the right.
With Jackson adding the conversion, Irish led 21-20 only to lose their way when Biggar stepped up.
Northampton ..23pts
Tries: Collins 8, Protcor 16
Conversions: Biggar 8, 16
Penalties: Biggar 2, 58, 74
NORTHAMPTON SAINTS: Furbank 7; Sleightholme 6, Proctor 8, Dingwall 6, Collins 6; Biggar 7, Mitchell 7; Auterac 6 (Waller 49, 5), Matavesi 6 (Fish 63, 6), Hill 5 (Harrison 56, 6), Coles 7 (Moon 65, 6), Ratuniyarawa 5, Wood 6, Ludlam 6 (c) (Lawes 54, 6), Augustus 7 (Painter 46, 6)
Not used: Lomani, Tuala
L Irish………………21pts
Tries: Creevy 37, Penalty 46, Parton 64
Conversions: Jackson 37, 64
LONDON IRISH: Parton 6; Loader 5, Rona 6, van Rensburg 6 (Williams 74), Hassell-Collins 7; Jackson 6, Phipps 6 (White 54, 6); Goodrick-Clarke 6 (Dell 56, 6), Creevy 6 (Cornish 46, 6), Hoskins 6 (van der Merwe 56, 5), Simmons 6 (Mafi 45, 6), Coleman 6, Rogerson 6 (c) (Nott 73), Donnell 5 (O'Brien 40, 6), Tuisue 4
REFEREE: Tom Foley
ATTENDANCE: 12,025
Star man
Matt Proctor – Northampton
