Cambridge completed a league double over Oxford this season - but how Darren Patterson's men didn't get a second goal in the second half only they will know.
In a two-minute spell just before the 80th minute, they laid seige to the visitors' goal and had four excellent chances to make it 2-2.
First Luke Foster's header was pawed away from the angle of post and bar by keeper Dammy Potter.
Then the keeper, back-peddling, turned over a chipped 20-yard shot from Jamie Hand.
From the corner, another Foster header had Potter scrambling to save down by his near post, and finally, from a fourth corner - all taken by Adam Murray - in barely 100 seconds, Craig McAllister had a header nodded off the line by Courtney Pitt.
It was a remarkable sustained spell of heavy pressure, but Cambridge held out, and won it courtesy of two Lee Boylan goals which took his tally to 11 for the season, and four in the last two games.
Third going into the game, Jimmy Quinn's men moved up to second place with this triumph.
They had been slightly the better team, but there wasn't much in it, which showed Patterson how far his side has come.
But there is still considerable room for improvement.
With Oxford's superb defensive record at home under Patterson, it came as quite a shock when Cambridge scored, in the 16th minute.
Rob Wolleaston, one of three former Oxford players in their varisty rivals' line-up, found space to cross from the left and Boylan, poorly marked 14ng a lost cause.
And when a second cross came in from Murray, following the flag kick, Potter dropped it, but McAllister planted his follow-up header from ten yards wide.
In the second half, though, Potter kept Cambridge in it after Boylan had grabbed a killer second goal.
It came on 57 minutes when Lee McEvilly got ahead of Barry Quinn to play the ball into Boylan, who created just enough space to turn and shoot beyond Turley for a good finish.
McEvilly was booked for his over-zealous celebration of the goal, which had particularly angered Turley.
Patterson made a double substitution just after the hour to try to get Oxford back on level terms, sending on Justin Richards and Yemi Odubade.
And Richards had a very presentable opportunity in the 90th minute from Odubade's right-wing cross, but headed too close to Potter, who palmed over.
A first defeat in four Blue Square games left Oxford fans frustrated - because this time they had created the chances. They just couldn't beat Danny Potter.
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