The match at Welford Road 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 and they held on.
Exeter fly-half Ignacio Mieres kicked all of the Chiefs' points as they beat Worcester 15-9 in a hard-fought game at Sandy Park.
Mieres and opposite number Joe Carlisle traded penalties before Exeter edged into a narrow 9-6 lead at half-time through the boot of the Argentinian.
Mieres then scored twice again to give the home side a nine-point lead before substitute Andy Goode kicked a late consolation for the Warriors.
Bath's stuttering season hit another low point as they surrendered a 10-0 half-time lead to lose 16-13 against Sale at the Rec.
It left the West Country club just seven points above bottom club Newcastle in the Aviva Premiership and, with a rash of injuries, they seem in no great shape to mount a convincing challenge against Heineken Cup holders Leinster next week.
Sale's match-winner was fly-half Nick Macleod who shrugged off some early misses with the boot before kicking three penalties and converting Mark Cueto's 54th-minute try.
Bath's points came from a Michael Claassens try, converted by Olly Barkley, who added two penalties.
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The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
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