Peter Horne’s last-gasp try saw Saints’ chances of European glory go up in smoke at Scotstoun as Glasgow sealed a 27-20 win.
Horne danced through the depleted Northampton defence, who were a man down after Alex Waller’s sin-binning, to win it for the Warriors in the dying embers of the game.
The defeat means Saints are out of the Heineken Cup and will not even make it into the Amlin Challenge Cup quarter-finals.
But it could all have been so different had they taken their chances during the first half of a game theyt dominated for long periods.
Dom Waldouck’s try, his first for Saints in 19 games since joining from Wasps last summer, and four points from the boot of Stephen Myler sent the away side in 10-6 up at the break.
Josh Strauss and Nikola Matawalu put Glasgow in front twice during the second period but George Pisi and Ben Foden replied for Saints.
And as Jim Mallinder’s men pushed for the all important fourth try and bonus-point win, they were stung by Horne’s heroics as he showed great poise to get over the line.
Saints will now be left to wonder ‘what if?’ as they return to domestic action, while Glasgow can spend their Saturday night toasting their first and only Heineken Cup win of the season.
The home side had rung the changes ahead of the game and they took just 24 seconds to open the scoring as Northampton-born Ruaridh Jackson landed a penalty.
Saints tried to show their teeth in the scrum, but the Scots stood strong, defending their territory defiantly. And it was to become a theme of the first half.
Glasgow’s good set piece work provided a platform for an attack, which resulted in another penalty for Jackson, and again he kicked it with ease.
Saints were having chances to respond, but a lack of sharpness between their backs was costing them tries.
Myler did at least ensure something came from the dominance as he delivered with a penalty, but the away side wanted more than three-pointers. They wanted tries.
Jamie Elliott almost got one, but his attempted slide over the line saw him hit touch before dotting down.
Nevertheless, Saints were signalling their intention to get much-needed scores that would help them on their way to a try bonus point.
Glasgow’s gritty defending was the source of great frustration for so long, but they hadn’t bargained for the sparky Waldouck.
The centre found a rare gap in the home side’s rearguard and burst through the middle to finally bring his team their first try of the day.
It was no more than Saints deserved but after Myler kicked them 10-6 in front, Glasgow came out fighting.
Stuart Hogg passed up the chance of a try before replacement Scott Wight, on for Jackson, who had been laid low by Samu Manoa, missed a penalty attempt from halfway.
Saints suffered a blow before half-time as influential back row Calum Clark was forced off with a suspected shoulder injury, spurring Mark Sorenson into action as a replacement.
Sorenson and Co needed a big second half to keep their Heineken Cup hopes alive, but Glasgow weren’t going to roll over and have their bellies ticked.
Instead, they emerged with aggression and with the bit between their teeth, the Warriors fought their way over the tryline, Strauss the scorer.
Wight converted and Glasgow could boast a 13-10 lead, giving them real belief that they could go on and take all four points.
Saints then suffered their second injury blow of the afternoon as Lawes limped off and the men in green, black and gold were really up against it.
Scrum-half Nikola Matawalu and full-back Hogg were causing plenty of problems, but Saints had a wildcard of their own, introducing Ryan Lamb.
The fly-half injected some tempo into his side’s game and after his fine kick just failed to find Elliott out wide, Lamb put in a good pass in the build-up to a fine try for Pisi.
The Samoan’s third score in two games against Glasgow, who will be sick of the sight of him, put Saints back in front at 15-13, as Lamb missed the conversion.
But Glasgow soon landed a sucker punch, with Foden left red-faced after handing the ball impressive No.9 Matawalu, who raced over the line to score.
Wight gave the Warriors a five-point lead heading into the final 10 minutes, but Foden was to immediately make amends for his earlier error.
The full-back took advantage of a great piece of awareness from Lamb to surge over the line and level the scores.
Lamb couldn’t add the extras, though, and Horne had the last word with a stunning try and easy conversion.
Glasgow: Hogg; Seymour, McGuigan (Horne 56), Morrison, Maitland; Jackson (Wight 34 (Dunbar 70)), Matawalu; Reid, MacArthur (Hall 51), Low; Swinson, Kellock; Strauss, Eddie, Wilson (Ryder 46).
Replacements: Grant, Kennedy
Saints: Foden; Wilson (May 56), G Pisi, Waldouck, Elliott; Myler (Lamb 56), Dickson (Roberts 59); Tonga’uiha (Waller 56), Hartley (Haywood 67), Doran-Jones (Mercey 56); Manoa, Lawes (Oakley 51); Clark (Sorenson 37), Wood, Dowson.
Referee: Leighton Hodges (WRU)