Cambridge came out on top in a game marred by five late red cards.
Exeter had Glenn Cronin and Gareth Sheldon sent off following a mass brawl in injury time in which UnitedÂ’s Shane Tudor and Tom Youngs were also dismissed.
Earlier Exeter goalkeeper Kevin Miller was shown red for a foul on Dave Kitson.
The Grecians had the first chance of the game in the eighth minute. Kevin MillerÂ’s long ball was flicked on by Steve Flack and Carl PetteferÂ’s cross was headed narrowly wide by young striker Lee Barnard.
Exeter took the lead in the 11th minute . Scott HileyÂ’s fine cross was met by Flack and his powerful header flew into the net.
Cambridge, who had scored in every league game so far this season, attempted to hit back and a Tudor corner was headed wide by Andy Duncan.
Youngs then skipped past two defenders and he drove a dangerous low cross into the box, but the ball somehow managed to elude everyone.
The visitors pulled level in the 34th minute. Youngs again skipped past Andy Roscoe and this time his cross was controlled by Tudor who buried the ball in the back of the net from ten yards.
Exeter should have been ahead five minutes after the restart. Roscoe found Pettefer in acres of space but with the goalkeeper to beat he struck the ball past the post.
James Coppinger launched a powerful run and when his shot was charged down Barnard thumped the rebound high over the bar.
But with only nine minutes left Kitson pounced on a mis-kick from George Pilkington and he calmly took the ball around Kevin Miller and stroked it home.
Exeter boss Neil McNab said: "I thought the refereeÂ’s performance was ridiculous, he just lost control. I was proud of my players and I am sad for them to lose that game."