Rob Dickie's first goal for his new club helped managerless Oxford United to a 2-1 victory over 10-man Peterborough for their first win in six matches.It was Posh's first defeat in eight games as they dropped out of the play-off places.Centre-half Dickie, signed from Reading in January, prodded the ball home from close range in the sixth minute when Peterborough failed to deal with James Henry's corner in the wind.Henry nearly doubled the lead moments later with a 20-yard drive that hit the inside of the post.And Henry did find the target with a superb finish after 61 minutes - from Ryan Ledson's pass - to put the U's two up.A minute later Steve Evans' men pulled one back when Jack Marriott turned in Marcus Maddison's cross for his 29th goal of the season.Maddison had earlier smashed an angled drive that Simon Eastwood saved with one hand, while Marriott drilled a shot narrowly wide late on.Peterborough skipper Jack Baldwin was sent off in stoppage time for a second yellow card.