Carlisle had to play for over an hour with ten men following an early sending off for Hallam Hope but in the end they were disappointed not to have taken all three points as they pondered a glaring late miss from substitute Derek Asamoah.
Mark Ellis was also given his marching orders as the clock ticked towards 90 minutes, having received two yellow cards, but the nine men deserved their point on what was a difficult afternoon.
Cambridge brought confidence into the game and they got the ball forward quickly as they looked to impose themselves on proceedings. The United defence held its shape and kept the doors closed and that forced James Spencer to shoot from distance. Ellis got in the way to make an important block.
A deep corner from Clarke found Legge on the jump at the back stick as the U's continued to go high but his downward header was hooked away by Grainger before Spencer could get a touch.
United had to defend when Berry burst clear on the left flank but Joyce did well to track back and he got the slightest of touches on what was an excellent cross. Ledson was frustrated as it was diverted away from his boot.
Joyce was there again when Dunk overlapped and crossed dangerously, and strong defending from Ellis and Miller in the follow up meant that Gillespie was once again protected.
An already difficult afternoon became that much harder for the visitors midway through the first half when Hallam Hope lunged into a challenge on Darnell Furlong. The referee calmed things down but immediately produced a red card.
The ten men reacted well and they should have taken the lead when Wyke reversed an inside pass into the area for Stacey to chase. He took a neat first touch and was a whisker away with a shot which crept under the keeper and just past the post.
A determined run from Furlong at the other end took him past two challenges but his cross had too much power and Spencer was a yard away from getting a touch.
The U's pushed the extra man forward and quickfire shots from Berry, Ledson and Spencer had to be smothered by some very brave defending.
Home pressure levels cranked up a notch as half time approached and good one-touch play left Dunne with a clear run through the middle. Ellis covered the yards to make another goal-saving challenge.
An offside flag stopped Ben Williamson’s celebrations in their tracks when he touched a Legge nod down into the net, and Spencer had Gillespie worried when he dropped a shoulder and clipped a curler at the back post. The ball dipped late but it was always heading wide.
There was more bad news for the Cumbrians on the stroke of half time when Raynes fell to the floor clutching his face having headed a high ball clear. He received immediate treatment and played no further part under expert advice.
Macaulay Gillesphey replaced Jack Stacey after the break as United went 3-4-2, but it was Cambridge who showed first when Furlong crossed from wide. Spencer won the header and Gillespie had to dive long to punch it away.
Carlisle had spells of their own and a poor clearance from Coulson presented Joyce with an unexpected opening 25-yards out. He let one fly and Norris had to dive to beat it away.
Spencer was weak and wayward with a poor shot when he was gifted space and time from a ricochet, but having soaked up everything the home side had to throw at them Carlisle were left wondering how they hadn’t got in front when a Grainger free kick spun into the air off the wall. Kennedy got there before the keeper and he quite literally put it on a plate with a lovely touch which found Asamoah just a yard off the line. The empty net gaped but the substitute leaned back and somehow lobbed his shot over the bar.
Carlisle escaped punishment for their howler of a miss when Simpson beat his man only to poke a shot wide, and Berry volleyed past the upright on the stretch when a cross from Ismail invited him to have a go.
Sweeney was then the hero when he cleared off the line as an almighty scramble followed a nod down from Berry, and United had to defend in numbers to preserve their point when yellow shirts flooded forward through a tense closing spell which saw Ellis red carded for a second bookable offence.
Cambridge - Legge (15), Furlong (73)
United - Wyke (8), Grainger (69), Miller (72)
Sent off - Hope (23 - straight red card), Ellis (83 & 90)
Cambridge United - Norris, Legge (Roberts 59), Berry, Dunk, Clark, Coulson, Dunne (Ismail 64), Spencer (Simpson 77), Williamson, Ledson, Furlong. Subs - Beasant, Omozusi, O'Neill, Williams.
Carlisle United - Gillespie, Miller, Raynes (Asamoah 45), Ellis, Grainger, Stacey (Gillesphey 46), Joyce, Kennedy, Hope, Gilliead, Wyke (Sweeney 77). Subs - Hanford, Ibehre, Comley, Thompson.
Referee - Mr Ben Toner
Attendance - 5,806 (403 away fans)