Chelsea and Leeds hate each other; it's as simple as that.
These days encounters between the two are few and far between so when they do meet in cup competitions, it is a big deal.
Wednesday night saw Chelsea travel to Elland Road for a quarterfinal tie in the Capital One Cup and it was expected to be a tough game for the Blues.
The first half certainly started that way, with Leeds taking a 1-0 lead into the break.
But in the second half, Chelsea's quality and class shone through and they gave Leeds nothing short of a battering, scoring five goals.
But what should we take away from this game, and what lessons have been learned about both clubs?