The match was contested by two teams of 14 for over an hour after Chris Ashton's clash with Alesana Tuilagi resulted in red cards for the Tigers winger and Northampton flanker Tom Wood.
Leicester led after tries from Matt Smith, Steve Mafi and Ben Youngs, Ashton with Northampton's only reply at that stage.
Tom May cut the deficit and Ashton set up Phil Dowson to put the Saints ahead for the first time since the opening 10 minutes, but Horacio Agulla edged the Tigers back in front late on.
After a spell of Northampton pressure which saw referee Wayne Barnes knocked off his feet by a runner, an offside infringement allowed Ryan Lamb to boot the Saints in front.
Toby Flood equalised in the 11th minute before the game burst into life.
Ashton, who was on the receiving end of Manu Tuilagi's infamous three-punch salvo in this fixture last season, had barged into a couple of physical challenges early on.
And it spilled over as Ashton tackled Tuilagi's elder brother Alesana out of play by his hair, sparking a fracas against the front of the stand which engulfed a dozen players and an unfortunate ball-boy, with Manu Tuilagi also attempting to get involved.
Despite not connecting with a punch, Alesana Tuilagi was red-carded along with Wood, who was spotted by the far-side touch judge throwing two punches. Agulla and team-mate Geordan Murphy were, like Ashton, fortunate to escape punishment.
A lightning Saints break led by Ben Foden was stopped by Smith's tackle on Ashton - and the centre again won the pair's battle at the other end, carrying the would-be tackler with him for several yards and superbly touching down right in the corner for the opening try. Flood's conversion attempt was wayward.
Foden diced with danger on his own line but touched down just before Smith's full-length dive could yield his second score, and a Tigers attack sparked by Youngs fell down when Flood's return pass was behind his scrum-half.
The second try came, though, when Foden's kick was charged down and he was forced to hack out for a line-out, from which Leicester recycled the ball and flanker Steve Mafi burst through four weak tackles for a converted score.
The collateral damage continued as Foden was tackled into a pitchside cameraman, before Lamb cut the arrears with a second penalty.
Flood missed a drop-goal and penalty on the stroke of half-time to leave it 15-6 at the break.
The England fly-half found the target early in the second half, but Ashton's fortunes turned when he was found by Foden on the end of some superb quick passing and went over in the corner.
Lamb missed the conversion and also a subsequent penalty from a central position.
Northampton were denied one of the tries of the season when they turned the ball over on their own line and from lock Courtney Lawes' wonderful pass, May broke the length of the field but was stopped by Mafi's last-ditch ankle-tap.
Youngs was injured in the aftermath but recovered to score Leicester's third try.
Lamb dropped a simple pass and Julian Salvi seized the loose ball and ran for the line. The Saints defence held firm until Youngs picked up and drove and was awarded the try on a marginal call by the television official.
May touched down in similar fashion to cut the deficit and replacement fly-half Stephen Myler rose above the kicking woes afflicting Lamb and Flood.
And Saints led 25-23 when Ashton recovered his own kick out of Agulla's hands and put flanker Dowson in behind the posts, Myler again slotting over.
But the game swung back the other way when number eight Thomas Waldrom shimmied and found Agulla, who ran 50 metres and mimicked Ashton's swallow-dive as he touched down.
Flood found his accuracy to put his side five ahead and they clung on.
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