Young striker Daniel Chillingworth made it three goals in two league games, and it was his second against Macclesfield which was decisive in Cambridge United's victory.
The Cheshire team had equalised with a Martin Carruthers' header in the 61st minute and were starting to run the game.
But Chillingworth's sharpness enabled him to take advantage of a defensive blunder just two minutes later, the spell was broken and the match transformed.
A back pass from Danny Adams forced Macclesfield keeper Boaz Myhill to try to boot the ball clear, but the young striker charged it down and ran it into the empty net.
Cambridge were able to consolidate and hold the lead, breaking just before the end as Macclesfield put everything into the search for a second equaliser, to grab a third goal.
Said Macclesfield boss David Moss: "The result was a bit of a travesty, we played so well and created as many chances as the team who could be among the front runners.
"Danny Adams, one of our most reliable players, made a mistake he will probably never repeat." But U's boss John Taylor, commented: "We had to battle a bit when they came at us in the second half but we played so well early on we could have been three up after 20 minutes.
"No doubt our second goal changed things, but they never really hurt us in the last 25 minutes." Three or four chances were squandered before Chillingworth combined superbly with Dave Kitson for his tenth minute goal.
Carruthers took his header well at the far post and had another tipped over the crossbar in the 87th minute.
But 60 seconds later two more of Cambridge's promising young strikers combined to wrap it up, Alex Revell firing home after teenager John Turner's shot had been blocked by the keeper.