|Leicester Tigers (12) 21|
|Tries: Veain, Toomua, Cons: Ford Pens: Ford 3|
|Northampton Saints (17) 27|
|Tries: Foden, Reinach, Tuala Cons: Myler 3 Pens: Myler 2|
Northampton inflicted a heavy blow on Leicester's play-off hopes with a dramatic victory at Welford Road.
Saints lost centre Rob Horne after just 13 seconds. He was taken to hospital after injuring himself as he attempted to make the first tackle of the game.
Despite the setback, Ben Foden and Cobus Reinach tries put Saints 17-12 up at the break, with Telusa Veainu and Matt Toomua going over for Tigers.
Ahsee Tuala's second-half try and two Stephen Myler kicks ensured victory.
Three George Ford penalties were not enough to help the Tigers avoid their first defeat in five games.
It leaves them fifth in the table with two games left to try to move back into the top four and secure a spot in the play-offs for a 14th successive season.
The East Midlands derby stalled immediately after kick-off with a lengthy delay in play as medics dealt with stand-in Saints captain Horne, who was floored with a head injury after colliding with Tigers lock Graham Kitchener as he collected the ball.
Saints, 10th in the table and looking for their first win in five games, then resisted the pressure heaped on them before a rampaging run from Paul Hill had Tigers scrambling in defence and Foden capitalised by going over in the corner.
Myler added a penalty to make it 10-0 before Tigers responded, with powerhouse England prop Ellis Genge offloading to Veainu to finish before Kitchener charged down a Reinach kick, which Toomua pounced on to score.
Reinach, however, ensured that Saints led at half-time, meeting an inside pass from Teimana Harrison to dart through Tigers' defence to score, and the scrum-half then set Tuala up for the first try of the second half.
Ford teed up two penalties either side of Alex Waller's yellow card for Northampton, only for Myler to land a decisive penalty of his own with 13 minutes remaining.
The home fans roared on the introduction of England international Ben Youngs on his return from a knee injury in a tense second half.
But, although Ford brought up 1,000 Premiership point with a 71st-minute penalty, the hosts fell short of victory when a late Jonah Holmes try was ruled out by the television match official for obstruction.
Leicester Tigers boss Matt O'Connor told BBC 5 live:
"It was a golden opportunity for us, not only for bragging rights in the derby but to keep ourselves in the mix in the top four, and that is what hurts the most.
"There were a lot of opportunities out there and the guys were really keen to put out a performance at home.
"We got a little carried away. We did an enormous amount of good things but didn't execute on the big moments. There were two or three definite tries there that we should have taken - you do that and we win comfortably.
On the Holmes effort ruled out late on: "It is something to raise with the officials, but realistically that didn't cost us the game. We probably dodge a bullet if it is awarded and we win, but it was a try all day."
Northampton winger Ben Foden told BBC 5 live:
"If you can't get up for a derby game you shouldn't be playing the game.
"Horne has been awesome for us on the field, he led us through the week and it was his first captaincy and was really looking forward to it. He made us think about the game and what we needed to do out there.
"Today we toughed it out and credit to the boys. There were times that we thought it might slip from our reach but we managed to score the tries when it mattered.
"The theme of our season is that we have been a 40-minute team or a 20-minute team and we have shown that we can beat the best sides. We needed an 80-minute performance and we did that today."
Leicester Tigers: Veainu; Thompstone, Smith, Toomua, May; G Ford, Harrison; Genge, T Youngs (capt), Cole, M Fitzgerald, Kitchener, Mapapalangi, Hamilton, Kalamafoni.
Replacements: Polota-Nau, Bateman, Mulipola, Wells, Evans, B Youngs, Worth, Holmes.
Northampton Saints: Tuala; Foden, Horne (capt), Francis, North; Myler, Reinach; Ma'afu, Haywood, Hill, Ratuniyarawa, Craig, Gibson, Harrison, Eadie.
Replacements: Clare, Waller, Painter, Paterson, Nutley, Mitchell, Burrell, Collins.
Referee: Matthew Carley.
Source: BBC Rugby Union News