Paul Lewis scored twice as unbeaten Cambridge beat 10-man Scunthorpe 3-2.
The U’s played with a numerical advantage from the 21st minute, when Scunthorpe’s James Perch was dismissed for a lunging challenge on Harvey Knibbs.
The visitors took a surprise lead four minutes before half time through defender Rory McArdle, who headed home unchallenged following Regan Slater’s corner.
Knibbs, earlier denied by a outstanding save by Rory Watson, marked his first career senior start with a goal seven minutes after the break.
Leon Davies’ superb cross from the right was knocked back across goal by Lewis to Knibbs, who converted from close range. Two minutes later it was Lewis who gave Cambridge the lead, slamming home after Greg Taylor’s cross fell to him.
Scunthorpe improbably equalised on the hour with McArdle once again heading home a Slater set piece from the right, only for Lewis to score his second to win it 17 minutes from time.
Sub Luke Hannant’s excellent cross from the left was converted by a thumping Lewis header.