Oxford then made it 2-0 five minutes later. Matt Robinson crossed from the left and Basham beat Marc Joseph to it to head past Fettis.
The City keeper was replaced at half time due to a knock, with Paul Musselwhite coming on to make his first appearance since January.
'Mussie' had little to deal with until the 65th minute when Alsop came in late on him from a corner. Following a scuffle, the referee showed the Oxford forward his second yellow card and they were down to 10 men.
Jamie Forrester was brought on for Stuart Elliott in the 73rd minute and Peter Taylor switched to a 4-3-3 formation. Four minutes later, the substitute passed to Danny Allsopp, and the Australian pulled it back to 2-1 with a low shot.
However, it wasn't worth anything in the end as Oxford held on for three points, and City were made to pay for failing to capitalise on early possession.
City line-up (4-4-2): Fettis (Musselwhite 45); Thelwell, Hinds, Joseph, Delaney; Price, Green, Ashbee, Elliott (Forrester 73); Burgess, Allsopp.
Un-used subs: Whittle, Melton, Keates.