The Saints' Champions Cup hopes now rest on a favourable result in the Challenge Cup final and a playoff, despite victory in a tense showdown with Harlequins at the Gardens.
The home side required four match points more than the Londoners to sneak into sixth place and seal automatic qualification, but come the final whistle the three-try, two-point margin was not enough and the visitors celebrated in defeat.
Saints got off to the worst possible start. A clearance from the kick off went out on the full and having marched some 40 metres back upfield for a lineout, Quins then went through the phases close to the home line, where James Horwill finally broke the Saints’ resolve.
The visitors were soon back with menace and while Saints were unlucky not win a penalty having quelled strong contributions from Marland Yarde and Chris Robshaw, a scrum went down, JP Doyle’s arm went up on the Harlequins side and Nick Evans slotted the simple three.
Just 10 minutes into a blockbuster tie and the next score was already looking imperative for the Saints. They duly got it. A big hit from Luther Burrell on Yarde won possession back in the Quins half and the big centre then crashed it up at pace before a beautiful inside flick from Mallinder sent George North behind the sticks.
It was a welcome tonic for the home side, as was a rare penalty miss from Evans, and a sublime kick in behind from Nic Groom then had Yarde in all sorts of trouble. Teimana Harrison, on for Tom Wood, made sure the scrabbling winger had nowhere to go and from the back of the resulting five-metre lineout, Louis Picamoles’ umpteenth offload of the game put Alex Waller crashing over.
Momentum was dipping back and forth and when Harlequins returned with vigour - Mike Brown breaking the home line - Joe Marchant snuck down the blindside to score.
While Evans refound his radar from the touchline having missed a second penalty, the three-point lead was short-lived. Burrell again provided the firepower and this time Mallinder’s contribution was a well struck penalty when Quins played the ball from an offside position.
With the two sides back as they had started turning around, it was down to a 40-minute shootout for the final Champions Cup place and while neither side came out of the blocks firing for it, Evans edged Quins back ahead to end a tentative scoreless period.
The Kiwi's departure injured shortly after, however, was to prove a turning point in the battle, if not in the war.
A trademark North break took Saints to within touching distance of a third try and while they then conceded a penalty under the posts, Tim Swiel's first contribution having replaced Evans was to miss touch. Ben Foden ran it back and Charlie Matthews soon found himself in the bin for a deliberate knock on.
Nafi Tuitavake's effort was ruled out for a forward pass in the spell that followed and a driving lineout was cynically pulled down by Joe Marler, allowing the 14 men of Quins to cling onto the lead by the skin of their teeth.
At the other end Swiel almost made amends, only denied by a fine tap tackle from Ace Tuala as he slalomed through the home defence during a breathless sequence.
Saints did well to scramble and then clear their lines, winning a penalty just outside the visiting 22 when Foden was hit by a swing arm from Horwill. Having gone for the corner, again they pitched their camp under the Quins posts and this time Api Ratuniyarawa provided the much needed power, smashing through a sea of bodies to score.
The men in black, green and gold were now a try away from the bonus win required, but a clear cut chance would not materialise.
Their chances will be pinned on a Stade Francais win over Gloucester in the European Finals next weekend, with playoff games to follow should the result go their way in Edinburgh.
3mins QUINS Try Horwill Con Evans 0-7
9mins QUINS Pen Evans 0-10
16mins SAINTS Try North 7-10
19mins QUINS Miss pen Evans
25mins SAINTS Try Waller Con Mallinder 14-10
32mins QUINS Miss pen Evans
35mins QUINS Try Marchant Con Evans 14-17
38mins SAINTS Pen Mallinder 17-17
HALF-TIME SAINTS 17-17 QUINS
50mins QUINS Pen Evans 17-20
69mins SAINTS Try Ratuniyarwa 22-20
FULL-TIME SAINTS 22-20 QUINS
Tuala; North, Tuitavake, Burrell, Foden; Mallinder, Groom; A Waller, Hartley, Brookes, Lawes, Ribbans, Gibson, Wood (capt), Picamoles
Haywood, Ma’afu, Denman, Ratuniyarawa, Harrison, Dickson, Olver, Hutchinson
Brown; Yarde, Marchant, Roberts, Visser; Evans, Dickson; Marler, Buchanan, Sinckler, Matthews, Horwill (capt), Robshaw, Wallace, Luamanu
Gray, Lambert, Collier, Merrick, Ward, Mulchrone, Swiel, Alofa