Cheltenham dented Cambridge's automatic promotion hopes with a last-gasp equaliser at the EV Charger Points Stadium.
United led when Sullay Kaikai lashed in a shot from the centre of the box in the 34th minute after Mamadou Jobe nodded a cross to him at the far post.
It was the highlight of an uninspiring first period, with Joe Day flying to turn over Kelland Watts' header from Kaikai's free-kick delivery just before the goal.
Cheltenham rarely threatened, with Josh Davison firing high over the bar at the end of a neat move involving Jake Bickerstaff and Isaac Hutchinson in the 27th minute.
Bickerstaff saw a shot blocked in the box after a charge forward from James Wilson early in the second half.
Louis Appere headed over James Gibbons' cross for Cambridge in the 65th minute and Day denied Ben Knight with an outstretched leg seven minutes later.
But Luke Young's cross was deflected into his own net by Jake Eastwood in the first minute of added time.
Match report supplied by PA Media.
