First-half goals from Jack Taylor and Kwame Poku set Peterborough up for a 2-1 victory at Oxford, who had striker Matty Taylor sent off.
Struggling Oxford had been hoping to follow up their big away win at Exeter seven days earlier but their form at the Kassam Stadium this season has been poor.
Irish midfielder Taylor turned in Ephron Mason-Clark’s left-wing cross in the seventh minute.
Posh doubled the lead on 31 minutes when Mason-Clark kept an attack alive by feeding Poku, who shot low past Simon Eastwood.
Billy Bodin, who had been unlucky with a goal disallowed for offside and a header against a post, pulled one back for the U’s on 52 minutes.
Marcus Browne headed across the area and Bodin nodded the ball back across keeper Lucas Bergstrom and into the net.
Taylor was red-carded for throwing Ronnie Edwards to the ground on 57 minutes.
Yet Oxford still went close to earning a point with Edwards blocking Browne’s shot on the goalline late on.
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