Veteran frontman Jabo Ibehre's first-half finish and some resolute defending earned Cambridge a 1-0 win at Crewe.
Strike partner Uche Ikpeazu was also a thorn in the side of the club, where he had previously spent three spells on loan, as the U's picked up their third win of the campaign.
Ikpeazu's physical presence caused Crewe problems before the break when his towering header dropped a yard wide. The big striker then propelled a looping header which was bound for the top corner until Ben Garratt scrambled across to paw the ball out of his goal.
But when the Crewe keeper could only spill Ikpeazu's snapshot from the edge of the box, Ibehre was on hand to finish from close range for the 35th-minute opener.
Crewe responded with Eddie Nolan's header dropping onto the bar and Chris Porter nearly forcing the ball home after David Forde failed to get a firm grip to youngster Tommy Lowery's stinging shot.
After the break try as they might Crewe struggled to make inroads into the visitors' rearguard which was held together by skipper Leon Legge and some confident handling from experienced keeper Forde.