Leicester (3) 11
Tries: A Tuilagi Pens: Flood 2
Northampton (0) 3
Leicester winger Alesana Tuilagi brushes aside Northampton's Chris Ashton to score the game's decisive try
Leicester booked their place in a seventh successive Premiership final after edging out Northampton.
Only a Toby Flood penalty separated the sides at the end of a thrilling first half which saw Tigers' Manu Tuilagi and Saints' Chris Ashton sin-binned.
Stephen Myler levelled for Saints with a penalty early in the second half, only for Flood to restore Tigers' lead.
And with nine minutes left Alesana Tuilagi went over in the corner to send Leicester to Twickenham yet again.
Reigning champions Leicester will now face either
Saracens or Gloucester
in the play-off final on Saturday, 28 May, while Northampton must lick their wounds and re-group before taking on Leinster in next weekend's
Heineken Cup final
But the Tigers may well head to Twickenham without centre Manu Tuilagi, who seems certain to be cited for punching Ashton in the altercation that resulted in both men being shown the yellow card eight minutes before half-time.
It started when Tuilagi tackled Ashton without the ball as Saints tried to take a quick tap penalty, resulting in an aggreived Ashton pushing Tuilagi in the back while he was on the floor.
Chris Ashton did go over and give him a push, but you cannot react with three punches to the head without a red card
Northampton coach Jim Mallinder on Chris Ashton's clash with Manu Tuilagi
The England Saxons centre responding by throwing three punches, the third of which connected with Ashton's face and left him needing treatment as blood poured from his eye.
It appeared to be a certain red card but on the advice of the touch judge the younger of the Tuilagi brothers escaped with a yellow, while a bemused Ashton was also shown a yellow card.
The game was still pointless at that stage, with defences on top, but it was certainly not without incident.
The first flashpoint came 12 minutes in when England team-mates Flood and Dylan Hartley clashed.
Saints skipper Hartley launched himself at the Leicester fly-half, who responded by going in with a swinging arm as both men hit the ground, but referee Wayne Barnes opted against brandishing his cards.
Flood missed the resulting penalty, but he finally kicked Tigers ahead three minutes before the break with both sides down to 14 men.
Leicester dominated the second half but could not break down the resolute Northampton defence and Myler and Flood exchanged penalties to leave both sides with all to play for going into the final 15 minutes.
The decisive moment finally came when Leicester replacement Thomas Waldrom threw out a speculative pass which Ashton just failed to intercept.
With the winger absent from his station front rowers George Chuter and Marcos Ayerza combined sweetly to free Alesana Tuilagi, the Premiership's leading try scorer this season, to rampage down the left.
Veteran New Zealander Bruce Reihana barred his way but Tuilagi blasted through his tackle and dived over to end Northampton's hopes of their first domestic and European double.
Leicester, meanwhile, are just one win away from completing only the second hat-trick in Premiership history - having achieved the previous one themselves between 1999 and 2001.
Northampton coach Jim Mallinder on whether Manu Tuilagi should have been sent off:
"First of all, you can't have players taking players out, and you can't be hitting players directly to the head, punching.
"Chris Ashton did go over and give him a push, but you cannot react with three punches to the head without a red card.
"It would have had an effect on the game, because they would have been down to 14 men. But Leicester played well in the second half - it is fine lines.
"When you come to places like this, you don't get the 50-50s. I think the referee did go to his assistant. All I know is I have seen it, and to me, it is a clear red card. What did Ashton get a yellow card for - pushing?
"It's a big game, live on television and it should be one of the highlights of the Premiership season. I guess the referees and referees' assessors will have a real good look at it and work as hard as they can to make sure it doesn't happen again."
Leicester rugby director Richard Cockerill:
"I was watching the ball, but the assistant referee clearly saw it and deemed it as a yellow card offence. I haven't seen the replays of it.
"It was a good performance against a really good side. Let's talk about that shall we? Let's talk about how we controlled the game, let's talk about Alesana's try, let's talk about the scrum contest.
"He (Manu Tuilagi) is a quality young player who does what he does exceptionally well. We will have to see what happens. We are guessing, aren't we?
"Our attitude to defend and not let them get any cheap points, and our tenacity at the breakdown was very good. We controlled the gain-line really well, and that was our best all-round performance for a long time.
"We wanted to put them under pressure. You stop them from getting on the front foot and they are not as effective as they can be."
Leicester: Hamilton; Smith, M. Tuilagi, Allen, A. Tuilagi; Flood, Youngs; Ayerza, Chuter, Castrogiovanni, Mafi, Skivington, Croft, Newby, Crane.
Replacements: Agulla for Smith (46), Grindal for Youngs (76), Cole for Castrogiovanni (53), Slater for Mafi (71), Waldrom for Crane (64). Not Used: Hawkins, Stankovich, Staunton.
Sin Bin: M. Tuilagi (31).
Northampton: Foden; Ashton, Clarke, Downey, Reihana; Myler, Dickson; Tonga'uiha, Hartley, Mujati, Lawes, Day, Clark, Dowson, Wilson.
Replacements: Geraghty for Myler (76), Easter for Lawes (71), Sorenson for Day (70). Not Used: Sharman, Waller, Mercey, Commins, Ansbro.
Sin Bin: Ashton (31).
Ref: Wayne Barnes (RFU).