Tigers ended Northampton's hopes of achieving their first domestic and European double at Welford Road - but their punishing play-off victory is likely to come at a price. Wing Alesana Tuilagi's late try and two Toby Flood penalties destroyed Saints' title dream.
Leicester though, could be without England World Cup candidate Manu Tuilagi - Alesana's younger brother - for a Twickenham showdown with Saracens or Gloucester on May 28.
Centre Tuilagi, 19, seems certain to be cited for punching Northampton's England wing Chris Ashton eight minutes before half-time of an East Midlands derby that rarely dipped below boiling point.
Tuilagi escaped with a yellow card, but the Rugby Football Union citing commissioner is unlikely to be as sympathetic after television replays revealed the full extent of Tuilagi's crunching right hook.
And Northampton will feel aggrieved that Leicester played the whole game with a full complement of players, given Tuilagi junior's reckless behaviour.
Saints are now left to focus on next Saturday's Heineken Cup final against Irish heavyweights Leinster in Cardiff as their solitary remaining hope of silverware this season.
And despite them throwing everything at Leicester in an attempt to nullify Tigers' revered physical power, it was not their day against opponents who deserved their triumph.
Leicester are one win away from completing the second title hat-trick in Premiership history - Tigers achieved the previous one from 1999 to 2001 - and they will inevitably take some stopping.
Leicester showed two changes from the side that secured regular season top spot by beating London Irish last Saturday, with number eight Jordan Crane replacing Thomas Waldrom and lock Steve Mafi preferred to Ed Slater.
Northampton, meanwhile, fielded 14 of the players that accounted for Heineken semi-final opponents Perpignan two weeks ago, as their solitary switch saw Bruce Reihana in for Paul Diggin.
The early exchanges were all about establishing close-quarter supremacy, although Northampton enjoyed territorial control as both packs got to grips with each other.
But it only took 12 minutes for the game's first flashpoint - and it involved England team-mates Flood and Dylan Hartley.
Saints skipper Hartley launched himself at the Tigers fly-half, hitting him late, before Flood responded by throwing a punch after both players hit the ground.
Referee Wayne Barnes opted against awarding a yellow card to either player, yet it would be no surprise if the RFU citing commissioner took a different view.
Leicester grew into the game, but Alesana Tuilagi - the Premiership's top try-scorer this season - was guilty of spilling two passes before Saints nullified a Tigers scrum deep inside their own 22 by snaffling possession.
The game did not lack for aggression, and it continued to simmer approaching the end of a scoreless opening 30 minutes, with Hartley continuing to wage war on any Tigers player who got in his way.
And tempers finally boiled over eight minutes before the break when Ashton and Tigers' England midfield hopeful Tuilagi got to grips.
Ashton appeared to push Tuilagi in the back of the head, then England Saxons midfielder Tuilagi punched Ashton and left him needing treatment.
Both players were sin-binned - Ashton trooping off with his head bandaged - yet Tuilagi, given an initial high-tackle and then three attempted punches, the last of which floored Ashton, unquestionably deserved a red card.
It proved a dreadful call by assistant referee Robin Goodliffe, who was barely 20 metres from the incident, but did not recommend a sending-off to Barnes.
Flood then opened Leicester's account with a 37th-minute penalty, giving Tigers a 3-0 interval lead, with the promise of a second X-rated 40 minutes to follow.
Saints struck first in the second period when Stephen Myler landed an equalising penalty, and with Tigers continuing to make scrummaging infringements - Italy international prop Martin Castrogiovanni was the chief miscreant - Northampton sensed set-piece dominance.
England prop Dan Cole replaced Castrogiovanni midway through the third quarter, before Flood missed a penalty and enabled Saints to keep a foothold in the contest.
Alesana Tuilagi though, then left Saints to concentrate exclusively on the Leinster clash next weekend when his touchline burst sent Leicester marching on and Saints trudging out of Premiership title contention.
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