Tom Craddock scored his 15th league goal of the season as Oxford beat relegation-threatened Lincoln 2-1.
The defeat means Lincoln need to win their last game, at home to Aldershot, to be certain of safety.
The Imps took an early lead and then struck the woodwork twice before the U's hit back.
Cian Hughton headed them into a fifth-minute lead from Gavin McCallum's left-wing cross before Luke Howell saw his fierce drive touched onto the bar by Oxford keeper Ryan Clarke.
And early in the second half, Ali Fuseini's chipped angled shot beat Clarke but hit the far post.
Oxford levelled on 61 minutes when Asa Hall volleyed in following a corner and Chris Wilder's men ended their run of four successive draws by plundering a 76th-minute winner when Craddock fired in from 14 yards.
Lincoln's woes increased further when centre back Danny Hone was sent off for a second yellow card, ten minutes before the finish.