Cheltenham and Oxford must still meet in the FA Cup replay and LDV Vans Trophy, but it's a draw and a win for Oxford from the series so far.
The result was tough on the home side who did the majority of the attacking but lacked the composure in front of goal to make their dominance count.
The first half began with a goal at each end, Oxford taking the lead when Eric Sabin broke clear on the right and crossed for Steve Basham to score with a tap-in after nine minutes.
Only two minutes later Cheltenham drew level when JJ Melligan found the space to centre from wide on the right and Steve Guinan levelled with a diving header.
Cheltenham went on to create some good chances in the remainder of the half, Oxford goalkeeper Billy Turley saving well from Kayode Odejayi and then from Guinan as the home side's wide men, Melligan and Brian Wilson, caused problems down the flanks.
But it was the visitors who scored the decisive goal against the run of play when Sabin rose highest to meet a cross from Lee Bradbury five minutes before the break. Cheltenham goalkeeper Shane Higgs touched the ball onto the crossbar but Sabin followed in to nod the rebound over the goal line.
Cheltenham attacked almost relentlessly during the second half but their reliance on the long ball and the efficient organisation of the Oxford defence left their forward line frustrated.
Guinan stabbed two shots over the crossbar and substitute Steven Gillespie also went close on two occasions but it was the Us who will return over the Cotswolds with confidence and three points from this encounter.