'You're not letting anybody else in, are you?' a Manchester City official asked of the club's stewards at the front entrance during half-time.
But by that point, the direction of travel was the other way. Plenty of Chelsea supporters had slouched off into the night and did not bother returning. Their bewildered team had been sent packing.
That was in part down to themselves - a rank display did nothing to calm talk around Graham Potter's credentials - although City more than had their say in it. After some stodgy performances so far this season, the 15-minute first-half blitz which saw them saunter into round four should act as some form of standard during the trickier weeks to come.