Injury-hit Saints suffered humiliation at the hands of London Irish as the Premiership strugglers sealed a 39-17 win at the Madejski Stadium.
Northampton, without 11 first-team players, had gone into the clash sitting pretty at the top of the table after five wins from as many games.
But they produced an ugly display, which saw Irish run in four tries to claim only their second win of the campaign.
Super centre Jonathan Joseph and hooker David Paice benefited from sloppy defending to send the home side in 18-0 up at the break.
Saints replied with a Stephen Myler penalty immediately after half-time, but things weren’t to get any better as Topsy Ojo and Jamie Gibson secured a deserved bonus point for Irish.
Ken Pisi and Phil Dowson grabbed late consolation tries for Saints and Myler added the extras, but it was far too little, far too late from the men in blue.
Steven Shingler put the shine on the Irish show with a late penalty, the full-back registering 16 points in all, with fly-half Ian Humphreys adding the other three with a drop goal.
It was to be a day of woe for Saints, which started when full-back James Wilson was ruled out with a muscle strain before kick-off.
That meant a reshuffle, with Noah Cato coming in on the wing and Vasily Artemyev, who was to have a torrid day at the office, shifting to 15.
Saints held the ball well in the early stages and the early possession produced a penalty as Irish were caught offside, but Myler was unable to slot, finding the distance but not the direction.
And the home side also missed their chance to put points on the board soon after as Shingler skewed his penalty moments later.
It was fairly nip and tuck for the first 20 minutes, until two big errors gifted Irish a score.
Mike Haywood misjudged a lineout, and after Marland Yarde gathered and kicked on, Artemyev made a howler, completely missing the ball behind his own try line, leaving Joseph to dot down.
Shingler again let Saints off the hook with the kick but the away side were not learning their lessons and the full-back did make them pay on 33 minutes, slotting a penalty.
By now the game was being played almost exclusively in the Saints half and Jim Mallinder’s men were losing every collision.
They were eventually punished further on 35 minutes as forward Paice barrelled over to score and Shingler made it a staggering 15-0 to the home side.
It was falling to pieces for Saints and Humphreys rubbed salt in the extremely painful wound with a drop goal to make it 18-0 before the break.
After what no doubt had been some ‘hairdryer treatment’ from Mallinder and Dorian West, Saints emerged strongly at the start of the second half.
And after a scything break from Pisi, the away side ground out a penalty, which Myler kicked to reduce the deficit to 15 points.
But Irish were straight back on the attack and more sloppy defending allowed Ojo to fly over and make it 23-3.
Ryan Lamb was introduced, putting Artemyev out of his misery, with Myler moving to full-back, before Shingler added to Saints’ suffering with another penalty.
Irish were taking sadistic pleasure in punishing the ineptitude of their opponents and they had more to celebrate on 61 minutes as Gibson broke clear to seal the bonus point.
Shingler added the extras before Saints got their first try of the game, with Pisi finishing off a flowing move.
Myler reduced the score further with the conversion, but Shingler’s penalty made it 36-10 with 12 minutes to go.
There was still time for another Saints try, from Phil Dowson, with Myler again on target from the tee.
But, fittingly, Irish and Shingler had the final say as the full-back kicked another penalty to complete a day of woe for Saints.
London Irish: Shingler, Ojo, Joseph, Tagicakibau (Armitage 66), Yarde; Humphreys (Geraghty 66), O’Leary (Moates 61); Lahiff, Paice, Aulika, Skivington (Low 75), Evans, Garvey, Gibson, Treviranus (Hala’ufia 61).
Replacements: Malton, Yanuyanutawa, Cotter
Saints: Artemyev (Lamb 50); K Pisi, Waldouck, Burrell (May 61), Cato; Myler, Dickson (Roberts 65); Tonga’uiha (A Waller 61), Haywood (McMillan 61), Mujati (Doran-Jones 61), Manoa (Oakley 61), Sorenson, Lawes, Wood (Harrison 61), Dowson.
Referee: Mathieu Raynal