Shane Geraghty was again left to rue a missed kick to win the game against Saracens
Saracens turned round a half-time deficit to end Northampton's 100 per-cent home record and pull to within two points of second-placed Saints with one league game remaining.
With Leicester certain to finish the regular season at the summit of the Guinness Premiership table after an emphatic defeat of Harlequins, Northampton could have guaranteed home field advantage for the play-off semi finals with victory on Saturday.
But Saracens played some scintillating attacking rugby at Franklin's Gardens with Ernst Joubert, Adam Powell and Rodd Penney all touching down in a 28-27 win.
With two minutes remaining, Ben Foden crossed for the Saints to add to their first half penalty try but for the second game running Shane Geraghty missed a kick to win the game as his off-target conversion ensured the Sarries left with the win.
Northampton travel to London Irish for their final regular season match in two weeks time while Saracens face an unenviable trip to Leicester who just need a bonus point to guarantee top spot.
The Tigers had few problems securing their position at the top of the table with a 40-22 victory over Quins at Welford Road.
Tries from Danny Care and George Lowe cancelled out Toby Flood's early score and handed the visitors a 17-16 lead at the interval.
But Leicester roared into the lead in the second half with scores from Matt Smith and Ben Youngs as well as a penalty try putting the hosts out of sight before young Quins prop Joe Marler crossed for a late consolation.
Meanwhile, the race for the final play-off spot remains wide open after Wasps and London Irish both slipped to defeats.
Gloucester dented London Irish's top-four ambitions with Lesley Vainikolo, James Simpson-Daniel and Alasdair Dickinson all touching down in a 34-20 victory at Kingsholm.
Meanwhile, Bath brought Wasps' three game winning streak to an abrupt end at Twickenham with New Zealand winger Joe Maddock grabbing a hat-trick of tries in a 35-19 win.
England hopeful Olly Barkley also impressed, kicking three penalties and three conversions as well as touching down himself in a victory which propels Bath above their opponents into fourth.
Peter O'Mahony was named man of the match against England last month
21 April 2017, 7:22pm
Peter O'Mahony's performance in the RBS 6 Nations finale for Ireland against England was crucial to his selection for the British & Irish Lions on Wednesday, Ireland and Lions defence coach Andy Farrell has revealed.