First-half Goals from Tyler Goodrham and Matt Phillips on his debut gave Championship new boys Oxford a 2-0 Carabao Cup win over League One Peterborough.
Posh were hoping to gain a measure of revenge for their play-off semi-final defeat by Oxford in May, but failed to convert good early chances.
Instead it was Oxford who took the lead in the 20th minute when Goodrham capitalised on a shocking error by visiting keeper Nicholas Bilokapic, who should have cleared a back pass first time but dithered. Goodrham tackled him and then tapped into an empty net from five yards.
Phillips doubled the lead five minutes before half-time, turning in Louis Sibley’s pass from the right after a fine U’s move.
Oxford made eight changes from the weekend win over Norwich, and Darren Ferguson three changes to his Saturday line-up against Huddersfield.
Posh had early scoring opportunities with Oscar Wallin heading a free-kick over then a corner straight at keeper Matt Ingram.
Ingram also saved from Archie Collins and Abraham Odoh.
The most spectacular effort came at the other end though as Bilokapic saved Goodrham’s curling 25-yarder at full stretch.
In the second half Ingram kept out low shots from Cian Hayes and Ricky Jade-Jones, while Odoh fired into the side-netting as the visitors searched for a way back into the game.
At the other end, substitutes Cameron Brannagan and Gatlin O’Donkor both went close to adding a third for Oxford late on.