The Black Cats took the lead when Corry Evans opened the scoring with a low shot in the 16th minute, yet U’s defender Elliott Moore headed the hosts level before half-time.
Both sides had chances in the second half before Sunderland substitute Elliot Embleton scored a dramatic winner two minutes from time.
The result moves Sunderland back up to sixth in the League One table with five games remaining.
Our chief SAFC writer Phil Smith has delivered his verdict on how each Black Cats player fared at the Kassam Stadium:
1. Anthony Patterson - 8
His save from Ciaron Brown in the second half defied belief and could be a pivotal moment in Sunderland’s season. Made another big save early on from Sykes. 8 Photo: JPI Media
2. Carl Winchester - 6
Didn’t always look completely comfortable but steady enough largely kept the opposition wing back at bay. 6 Photo: JPI Media
3. Bailey Wright - 7
Beaten by Moore for the equaliser but otherwise defended both well and tenaciously. 7 Photo: JPI Media
4. Dennis Cirkin - 5
Started very well defensively but tired as the game went on and Oxford might feel they should have got more joy from their forays down the right flank. 5 Photo: JPI Media