And they did it despite playing with only 10 men for the whole of the second 45 minutes after striker Jon Shaw had been sent off in first half injury time.
The striker, who had given the Shaymen the lead from the penalty spot, was dismissed after clashing with Cambridge defender Michael Morrison.
And within 10 minutes of the re-start the home side had hit the front for the first time in the game.
But Halifax refused to buckle and an enterprising display was rewarded seven minutes from time when Cortez Belle blasted home his first goal for the club.
It was no less than Chris Wilder's men deserved as even with a man short they matched their hosts - and they even had the chances to take all three points.
Town were the better side in the opening quarter with Greg Young heading a Tom Kearney corner over the top and Shaw let down by his first touch as he latched onto an Anthony Griffith through ball.
And they took the lead after 18 minutes when Shaw got up off the floor having been dumped there by Morrison to send United keeper Danny Potter the wrong way from the penalty spot.
Within six minutes, Cambridge were level when the Town defence failed to deal with a Courtney Pitt cross from the left and Marvin Robinson slid the ball home at the far post.
Lewis Killeen and Shaw combined to create an opening for Daryl Taylor, but his effort from a tight angle was easily saved and Killeen was forced wide of the goal after racing onto an Alex Bailey ball soon after.
Griffith was inches away from connecting with the ball six minutes before the break after Taylor and Matt Doughty had cut open the home side down the left.
And United's only real glimmer of hope came when a couple of weak headers from Belle and Young put Adam Legzdins in trouble, but he cleared his lines.
Town suffered a major blow on the stroke of half time when, a minute after he had been booked, Shaw was shown a red card after jumping across Morrison who initially looked to be injured, but soon recovered.
And the home side enjoyed the better of the opening minutes of the second half with Robinson heading down and wide before they took the lead in the 55th minute, Rob Wolleaston firing home from 25 yards.
Most people in the ground thought Cambridge had bagged a third two minutes later when, after Legzdins had saved magnificently from Stephen Reed, Robinson forced home the rebound.
But the Shaymen were saved by the linesman's flag which was raised on the near side.
Daniel Gleeson then flashed a shot across the fare of goal but wide of the target and there were a couple of other opportunities with Scott Rendell going closest, firing a left foot shot off target.
Substitute Steve Bushell almost made in immediate impact when the ball fell to him on the edge of the area, but Morrison raced out to block the shot.
And a great run from Kearney with 16 minutes remaining gave Taylor the chance to beat two defenders before he was denied by home keeper Potter.
Three minutes later Kearney's corner picked out Belle eight yards from goal, but his downward header went straight into Potter's hands.
There was a real heart in mouth moment with 10 minutes to go when a Young back pass fell short and Legzdins raced off his line. Robinson went over the keeper's outstretched legs and the referee raced to the incident with his hand in his top pocket.
As the home crowd waited for a red and a penalty, he produced a yellow for a dive and gave the Shaymen a free kick.
Within three minutes Town were level. Doughty launched the ball into the area from a throw-in and Killeen got a touch before Belle hammered it into the roof of the net, giving Potter no chance.
Remarkably, both sides had opportunities to win the game late on.
Legzdins produced a wonderful save to keep a Pitt header out and Robinson headed wide before Lee Boylan got away only to be denied by a Young block.
And at the other end, Taylor's pace caused more problems for the home defence with Mark Peters and Potter getting in a real tangle.
Taylor spotted that the keeper was way off his line - he was on the edge of his own area - but his curling shot from the left hand side bounced into the side netting.