Ciaron Brown headed a dramatic stoppage-time winner as Oxford came from behind at half-time to beat Cambridge 2-1 at the Kassam Stadium.
Jordan Cousins fired Cambridge ahead in the 30th minute, prodding the ball in at the back post when Oxford failed to deal with a corner.
Tyler Goodrham levelled with a superb solo effort nine minutes after the break, cutting in from the left touchline and firing past Jack Stevens into the far corner from 22 yards.
In the fifth minute of added time, defender Brown headed home after Stevens could only push out Cameron Brannagan’s 20-yard drive.
James Brophy should have doubled Cambridge’s lead soon after Cousins’ opener, only to head Danny Andrew’s cross past the post.
Oxford keeper James Beadle then saved at full stretch from Sullay Kaikai.
The home team responded, with Stevens saving from Goodrham and Stan Mills.
Des Buckingham’s side pressed hard for a winner and it took two fine saves from Stevens to deny Brannagan, before he was eventually beaten with just seconds remaining.