Northampton claimed East Midlands bragging rights and a place in the Gallagher Prem final after eventually subduing Leicester in a thrilling 45-31 victory at Franklin's Gardens.
Tom Litchfield ran in a first-half hat-trick, George Furbank crossed twice on his home farewell ahead of his move to Harlequins and Tommy Freeman and Archie McParland also touched down as Saints booked their place at Allianz Stadium next Saturday.
Leicester were magnificent with Ollie Hassell-Collins pouncing for two of their five tries and their refusal to concede defeat even as they chased down hefty deficits contributed to a frantic and brilliant play-off.
But Northampton were electric in attack to signal to Bath and Exeter, who meet on Saturday, that having finished the regular season as league leaders they are also the team to beat at Twickenham.
The speed, accuracy and ambition of their play was mesmerising and they have now amassed 111 tries in the Prem in 2025-26, although it was not until Furbank raced over for the second time with six minutes left that they could rest easy against Tigers.
England head coach Steve Borthwick watched from the stands as a number of his players - from both teams - starred on a thrilling night, but it was Fin Smith who finished as man of the match with Henry Pollock surely close behind.
Having been booed on to the pitch by the noisy home crowd, Leicester faced a similar onslaught when play begun with Pollock heavily involved as Litchfield used his athleticism to glide over after just 87 seconds.
The early score was a signpost for the mayhem to come with four tries arriving in 13 high-octane minutes that saw the lead change twice.
Leicester hit back with a Hanro Liebenberg pick and go and then Freddie Steward crossed with an outstretched hand on his comeback from a broken thumb following an innovative Tigers set play.
Saints rallied when Litchfield struck again with help from a mix-up between Steward and Billy Searle and in the 20th minute they opened up daylight when Smith darted forwards and chipped ahead of Freeman to touch down.
Provided with quick ball by a home pack that was shading the forward exchanges, Smith was taking charge while Pollock was everywhere.
But a pulsating first half produced two more twists with Hassell-Collins finishing a Searle kick-pass before Litchfield completed his hat-trick by muscling over from close range following a break by Freeman.
Saints opened up daylight once again early in the second half when Furbank picked his moment to strike off Rory Hutchinson's slick passing, but Leicester refused to throw in the towel and they created the space for Orlando Bailey to cross.
The Tigers had the wind in their sails but they could not capitalise on a dominant spell, although they at least defended their line when they came under pressure with Steward saving them in the right corner.
Pollock was left shaken by big hit from George Martin but Saints were back on top, helped by the hard yards from South African giant JJ Van Der Mescht off the bench, and in the 66th minute they were over again with McParland rounding of an electric attack.
Leicester were still throwing, however, as Hassell-Collins touched down a Searle kick, but Furbank landed the killer blow when he sprinted across the whitewash after Freeman had burst forward.
Northampton boss Phil Dowson praised Pollock's growing maturity after the England back row played an influential role in Saints' win.
A month ago the 21-year-old British and Irish Lions player was criticised for a fiery cameo off the bench in a 41-17 rout by Leicester that saw him become embroiled in several flashpoints.
But Dowson said: "Henry was excellent and what pleases me most is that - I'm not going to use the word vilified - a lot of flak came his way after the game at Welford Road.
"You can talk about loads of things that Henry does really well but his ability to learn from experience and apply that very quickly and effectively, how he talks to referees has changed in probably about three weeks.
"How he deals with confrontations has changed a little bit as well. I hope that gets noticed, as well as how quickly he matures and makes those decisions. I'm really pleased that he's a bright lad.
"His power per kilogramme is nuts, as are his ability to beat players with his speed and his ability to understand when to pass the ball and when not to.
"He's never looked for controversy. I don't think he's gone out there and gone, 'I'm going to wind up Ollie Chesham and see what happens here'.
"He's under more scrutiny than probably anybody else potentially in the league and I think he's dealt with it really well."
