Newcastle claimed a dramatic stoppage-time victory at Welford Road to deny Leicester and keep themselves firmly in the Aviva Premiership playoff race.
No. 8 Ally Hogg's try, which was reviewed at length by the television match official, and replacement scrum-half Sonatane Takulua's conversion, edged Newcastle home 25-23.
It took them third in the table with one game left, but Leicester, who have not finished outside the Premiership's top four since 2004, are facing playoff heartache.
Tries by wing Jonny May and lock Mike Fitzgerald -- plus 13 points from fly-half George Ford's boot -- appeared to be enough for Leicester as Newcastle chased a first win on Tigers soil for 20 years under their rugby director and former Leicester boss Dean Richards.
Newcastle's ex-Leicester wing Vereniki Goneva scored two tries, while fly-half Joel Hodgson added a conversion and penalty before going off injured and Juan Pablo Socino landed a penalty.
And the Falcons -- thanks to their late, late, show -- remain in control of their own destiny ahead of hosting Wasps next weekend.
Leicester, meanwhile, must beat Sale Sharks, but even that is unlikely to be enough as Newcastle and Wasps are now favourites to join Exeter and Saracens in the semifinals.
Despite the stakes being so high, neither side had any intention of opting for a safety-first approach as two tries arrived inside the opening seven minutes.
Newcastle claimed the opener through Goneva, who broke clear from the base of a ruck 40 metres out and left Leicester's defence in reverse gear for a superb solo touchdown that Hodgson converted.
Leicester, though, responded impressively, establishing a threatening position when flanker Brendon O'Connor made initial headway, and quickly recycled possession resulted in centre Manu Tuilagi, on his return to action after five weeks out injured, sending May over.
Ford kicked the touchline conversion to make it 7-7, yet Newcastle quickly regained the lead when Hodgson booted a penalty after Leicester flanker Luke Hamilton was punished for killing possession.
Ford then tied things up with a penalty, but the injury count began to mount up for Newcastle as Hodgson limped off to follow earlier injury departures of prop Scott Wilson and lock Sean Robinson, which tested their resources and resolve.
A second Ford penalty edged Leicester ahead nine minutes before the break, only for Newcastle to finish the half strongly and set up camp inside Leicester's 22.
And they gained their reward through a Socino penalty, making it 13-13 at the interval and setting up an intense second 40 minutes as both sides fought for vital league points.
Leicester thought they had regained the lead early in the second period after they broke clear from a scrum near their own line, Newcastle fumbled in defence and Ben Youngs kicked ahead to touch down.
But referee Luke Pearce, after consulting with television match official Stuart Terheege, ruled a Leicester knock-on before the move began and Newcastle escaped.
It was a short reprieve for Newcastle, though, and Leicester scored from their first attack, sending a wave of ball-carriers at Falcons' defence before Fitzgerald stretched out and claimed a try that Ford converted.
Ford completed his penalty hat-trick to ease Leicester's nerves, and although Goneva breached their defence for a second time 11 minutes from the end, it still looked all up for Newcastle until Hogg and Takulua came up trumps after Tigers No. 8 Sione Kalamafoni was sin-binned.