Tayo Edun's superb free-kick earned Peterborough a 1-0 League One success at Cambridge.
Edun's 22-yard strike 18 minutes from the end left Nathan Bishop with no chance and ensured Posh did the double over the U's for the second successive year.
The goal came against the run of play, with relegation-threatened Cambridge guilty of missing a number of big chances.
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Jordan Cousins had forced Jed Steer into a save with a strike from long range, and in the final minute of the first half Steer made a point-blank stop from Dom Ballard when he was teed up by James Brophy following Ryan Loft's nod down.
Just before the hour Ballard rolled his man and bore down on goal before blazing over, and after 66 minutes Scott Malone also hooked a volley off target.
Looking to respond after Edun's goal, substitute Dan Nlundulu fired straight at Steer.
Edun was sent off in the final seconds of injury time for a second yellow card but Cambridge remain 12 points from safety.