Newcastle finished bottom of the Premiership table despite beating Wasps on Saturday, while Northampton reached the play-off semi-finals.
Newcastle face relegation despite their crunch basement battle against fellow strugglers Wasps ending with a hard-earned 14-10 victory.
The Falcons finished bottom by a point following a 22-game regular league season that saw them win just six matches.
They needed a bonus-point triumph over 11th-placed Wasps - and also deny their opponents a losing one in the process - but that fanciful script never seriously looked like unfolding at a packed Adams Park.
Wasps, relieved to start putting an injury-ravaged campaign behind them, saw wing Christian Wade claim his ninth league try of the campaign, while fly-half Nicky Robinson added a conversion and penalty.
Centre James Fitzpatrick touched down for the visitors midway through the second period, a try that Jimmy Gopperth converted, yet a game suffocated by tension had no chance of breaking into the free-scoring spectacular that Newcastle needed.
Even when scrum-half Peter Stringer touched down late on, with Gopperth adding the extras, there was no obvious sign of any further late drama.
Falcons' fate now rests on the outcome of this season's second-tier Championship title race, which will not be concluded until May 30.
Bristol, London Welsh, Bedford and Cornish Pirates are all contesting silverware, although it is thought only Bristol of that quartet categorically meet Premiership entry criteria.
Chris Ashton's Franklin's Gardens farewell lasted only 19 minutes but it was long enough for the England winger to score the try which set Northampton on the way to the Aviva Premiership play-off semi-finals for the third successive year with a 42-14 win over Worcester.
Saracens-bound Ashton took only five minutes to mark his final home appearance with a try before retiring hurt 14 minutes later.
England full-back Ben Foden, winger Paul Diggin and replacement forwards Teimana Harrison and Alex Waller scored Northampton's other tries with fly-half Stephen Myler kicking 10 points and his replacement Ryan Lamb booting seven.
Worcester replied with a tries from left-wing Josh Drauniniu and number eight Kai Horstmann, both converted by fly-half Danny Gray.
The victory clinched fourth place in the Premiership table for Saints as they joined Harlequins, Leicester and Saracens in the play-offs.
Harlequins secured top spot with a 24-10 triumph over Sale in the Sharks' last ever game at Edgeley Park.
England internationals Danny Care and Mike Brown went over in the first half as Quins established a 15-3 advantage at the interval, with Nick Evans adding a conversion and a penalty.
Tommy Bell responded for Sale with a penalty before two second half Evans' three-pointers extended the visitors' advantage.
Will Addison crossed for the Sharks to give them hope, but a further kick from the tee sealed the win for Harlequins and a home semi-final in the play-offs.
Billy Twelvetrees showed what Leicester will miss next season when he helped the Tigers book a home semi-final with a comfortable 28-3 win over Bath.
The 23-year-old England Saxon centre, who is leaving for Gloucester at the end of the campaign, replaced the injured Toby Flood at half-time and helped Leicester turn a 3-0 half-time lead into a 28-3 victory at Welford Road.
Twelvetrees kicked 10 points and created two of the Tigers' three tries in a win which earned them a semi-final next Saturday at home to Saracens, the team they have played in the last two finals.
Anthony Allen and Horacio Agulla both crossed for the Tigers, who were alos awarded a penalty try.
Saracens gave a convincing second-half performance to run out comfortable 40-22 winners over Exeter at Vicarage Road.
The home side trailed 10-9 at the interval but two tries early in the second half gave the hosts the impetus they needed.
The bonus-point victory was not enough to secure Saracens a home semi-final in the Aviva Premiership play-offs because of Leicester's home win over Bath, and they now face a difficult trip to the Tigers next weekend for a place in the final.
Rhys Gill, Charlie Hodgson, Alex Goode and James Short all crossed for the hosts, with Owen Farrell converting them all and adding four penalties.
Matt Jess, Tom Johnson and Chris Budgen replied with tries for Exeter, with Gareth Steenson slotting over two conversions and a penalty.
London Irish gave England-bound attack coach Mike Catt the perfect send-off with a six-try 52-18 win over Gloucester in a Madejski Stadium contest marred by the sendings off of Jim Hamilton and David Paice.
The game was effectively over by half-time as tries from Darren Allinson, Sailosi Tagicakibau and Jonathan Joseph, plus a 19-point haul from Tom Homer, put Irish 34-11 ahead.
Homer kicked another penalty while substitute Marland Yarde (2) and the departing Delon Armitage added further tries to complete the rout.
Two Tom Voyce tries and eight points from Freddie Burns were all Gloucester had to show for their efforts as they suffered a sixth-straight defeat to hand Mike Tindall a sad end to his Kingsholm career.