Defeat all but extinguished Northampton's hope of a successful title defence, with this reverse leaving the Saints eighth in the 10-team table and nine points adrift of a top-four finish that will guarantee a play-off spot.
Northampton were without several of the internationals who helped England end the Six Nations in second place, with Alex Mitchell and Tommy Freeman rested, while their fellow back Ollie Sleightholme was injured.
They have struggled with the absence of several veteran forwards who called time on their Saints' careers after last season's title triumph, including former England captain Courtney Lawes.
But it was a surprise that Leicester, who moved into third place ahead of Saturday's matches, scored three tries in the opening 13 minutes at Franklin's Gardens through Adam Radwan, Jack van Poortvliet and Olly Cracknell.
Handre Pollard, a World Cup-winning fly-half with South Africa, added two penalties either side of the half-hour to make it 23-0 to the Tigers before Charlie Clare's intercept saw Leicester secure a try bonus-point with four minutes remaining.
Sale recorded their first Premiership win of 2025 with a 39-15 victory away to northern rivals Newcastle.
Sale were 17 points ahead at half-time thanks to tries from Bevan Rodd, Rob du Preez and Tom O'Flaherty and two penalties from returning veteran England fly-half George Ford.
Despite being reduced to 14 men in the second half at Kingston Park, Joe Carpenter scored Sale's fifth try as they maintained their challenge for a top-four finish.
But Newcastle's 10th defeat from 12 league games left them rooted to the bottom of the table.
Saracens play London rivals Harlequins on Saturday when leaders Bristol face Exeter in a west country derby.
Bath take on fellow southwest side Exeter on Sunday.