Crewe skipper Ashley Westwood was sent off as Steve Davis' first game in charge ended in a 4-1 FA Cup defeat by Colchester.
Davis replaced Dario Gradi in midweek after the 70-year-old called time on a distinguished career.
His team opened the scoring in the 18th minute when Byron Moore smashed home after Ajay Leitch-Smith's shot had been saved by Ben Williams.
But Westwood ultimately ruined the home team's chances of victory two minutes later by getting himself sent off for a nasty two-footed lunge on Ben Coker.
Lloyd James brought the U's level in the 59th minute with a 35-yard wonder-strike that rocketed in off the underside of the bar.
Andy Bond grabbed the second on 77 minutes when he sidefooted home from a corner, Coker fired low and hard into the bottom corner for number three 10 minutes later and James notched the fourth in stoppage time.