Obviously the 4-0 against Real Madrid but there are two others for me that spring to mind. The 7-2 against Stoke in 2017 was the game that really announced the Centurions team. We dominated the first half and it was only two deflected goals that brought them back to 3-2 however that only poked the bear and Kev was magnificent all game until Pep decided to declare after 70 minutes and take him off. If it had finished 12-2 that day I would have said it was a fair reflection of the game.
The other one is a bit more obscure, someone mentioned earlier in the thread the 2-0 win at Leeds on Boxing day in 1976, a game at which I went to but got locked out off because the coach arrived too late and we were locked out. However the previous game against Coventry at Maine Road we tore them apart. It finished 2-0 but should have been at least 8 but for their keeper and us not taking our chances, sound familiar!