Wrexham bounced back up to the second division at the first attempt as they booked the third automatic promotion spot.
Their romp against the U's took their run to seven straight wins and delighted the nearly 10,000 happy fans who turned up for the party.
Police appealed for fans to keep off the pitch but several thousand poured from the kop and the stands at the end in a good humoured celebration, then watched the players receive the promotion champagne to rapturous applause.
A three-goal blitz in seven minutes midway through the opening half set the promotion party going and it was only a formality when two more goals were added in the second half.
A dispirited Cambridge finished with 10 men after substitute David Theobald was sent off for his second bookable offence. It completed a nightmare for him after he had been blamed for two goals.
Paul Barrett fired the opening goal from ten yards, Brian Carey headed the second from Darren Ferguson's corner and Ferguson set up another third with a corner which Carey nodded down for Steve Roberts to finish off.
Wrexham brought on substitute Kristian Rogers for the second half but he had no more to do than had Andy Dibble before him, making one good save to keep out a 30 yard shot from Luke Guttridge.
Paul Edwards chipped the fourth on the hour and then turned provider for Lee Jones to complete the rout two minutes later.
Wrexham manager Denis Smith said: "It's been a very enjoyable day and a big achievement. We have done it in style." "They said you had to kick your way out of this division, but we have done it by playing good football and scoring goals." Now he sees his main task for the future as keeping all his players together when they go up to the second division.
Cambridge boss John Taylor said: "I'm obviously disappointed with our performance. We were very poor today. Individual mistakes cost us at least four goals."