Ben Botica inflicted late heartbreak on Saints as his last-gasp score handed Harlequins a 31-30 win in the LV= Cup opener at Franklin’s Gardens.
The fly-half dotted down after the clock had gone dead and then kicked the conversion to ensure his side won the contest by the narrowest of margins.
Saints were made to pay for a first half horror show as they slipped 21-6 before recovering to make it 30-24 with seconds to go.
But tries from Luther Burrell and Tom May were only enough for a losing bonus point as Sam Smith’s double, Harry Sloan and Botica won it for the Premiership champions.
It was a Jekyll and Hyde showing from Jim Mallinder’s shadow side, whose defeat means Saints have now lost four games on the bounce.
Their first-half performance was to blame for this defeat and Lamb was the main culprit as he played a part in both of Quins wing Smith’s scores inside the first 35 minutes.
Mike Haywood also gave the Twickenham-based side a helping hand, overshooting a lineout which centre Sloan capitalised on to score.
Lamb kept his men in it with three successful penalties, his kicking from the tee the antithesis of his form in open play.
And that provided Saints with the catalyst for a superb second-half comeback as scores from Luther Burrell and Tom May and eight points from the boot of Lamb completed the recovery.
But Ethan Waller’s late yellow card gave Quins the shot in the arm they needed as Botica won it.
Ahead of the game there was a minute’s applause for former Saints prop Nigel Fox who tragically died earlier in the week, and a period of silence ahead of rememberance day.
It was fitting that on a day which saw so many of Northampton’s next generation of players on the bench - and academy centre Tom Stephenson making his first-team debut - one of the club’s old guard should be remembered.
Saints came out of the blocks the fastest as Quins tried to hold them up a penalty was conceded, handing Lamb the chance to lash the ball between the posts for 3-0.
But Quins were gifted the chance to get their noses in front as Paul Doran-Jones fumbled a poor pass from Lamb in midfield and Smith picked up, waltzed through a couple of weak challenges and dived over.
Botica added the extras, prompting a test of Saints’ steel and they replied through another Lamb penalty after crushing Quins in the scrum.
A sloppy spell of play then unfolded, culminating in a horror show for the home side as Haywood’s erratic lineout gave Sloan an easy score.
Botica again notched the extras, leavng Saints 14-6 down thanks to two moments of defensive slumber.
Northampton were in desperate need of a spark, something to click them out of the daze, but things weren’t going their way as Lamb’s penalty inside halfway hit the post.
And things were to go from bad to woeful for Lamb and Saints moments later as the fly-half was left red-faced after seeing his errant pass intercepted by Smith who scored his second of the game.
Groans rang out around the Gardens, with Lamb left on his haunches, pondering what had just happened as Botica put Quins 21-6 up.
A nightmare 40 minutes came to and end on a slightly brighter note for Saints as Lamb landed another penalty to bring them back to within 12 points, but a big second half was needed.
Lamb got the ball rolling with another penalty and after gathering the restart, Saints hauled themselves back to within four points of their opponents as Burrell picked up a pass from Jamie Elliott and put in a powerslide to get over the line.
Lamb missed the conversion but the relief was palpable as Northampton had ended a run of two and a half games without a try.
Christian Day made his comeback from injury, replacing Rhys Oakley, but his appearance was only to last 11 minutes as he limped off.
Quins extended their lead against as Botica blasted another penalty over but Saints were looking like a different side and they soon had a second score to their names as Burrell ofloaded to May, who darted over the line.
Lamb converted and the scores were level, with Quins suddenly looking punch-drunk.
And they were on the canvas at 27-24 down moments later as Saints’ No.10 again put boot to ball with good effect, finding the target with another penalty.
Mallinder then took the chance to hand game time to youngster Ethan Waller, who engaged in a handshake with brother Alex before replacing his fellow prop.
Saints continued to turn the screw up front, with penalties at the scrum in their favour approaching double figures.
And Lamb made the most of the territory earned by the forwards, slotting a drop goal to put his side six points ahead with three minutes to go.
But Saints couldn’t get over the line as Waller saw yellow with his side under pressure and Botica made them pay with a score in overtime, kicking the conversion to win it by a point.
Saints: May; Armstrong, Stephenson, Burrell, Elliott; Lamb, Roberts; A Waller (E Waller 71), Haywood (McMillan 71), Doran-Jones (Herriott 78); Sorenson, Oakley (C Day 51 (Harrison 62)); Clark, Nutley, van Velze.
Replacements: A Day, Mogensen, Collins
Harlequins: L-Hague; Stegmann, Hopper, Sloan, Smith; Botica, Dickson; Lambert (Marfo 70), Ward (Buchanan 48), Collier (Sinckler 70); Browne (Twomey 70), Matthews; Trayfoot (Clifford 70), Wallace, Guest
Replacements: Burns, Grimoldby, Mantella
Referee: Neil Hennessey (WRU)