The Baggies gloveman produced a string of fine saves to deny the Reds in his sides 2-0 win at Anfield as well as denying Steven Gerrard from the penalty spot when it was still 0-0 and he suggests it was his best-ever showing.
"That penalty save probably just made it the best," said Foster.
"I played well in that game and the Carling Cup final was great when Birmingham beat Arsenal in 2011.
"But with the penalty save and the fact we were playing at Anfield, that performance probably just tops it.
"There was also the fact we needed the win so badly which was probably just the icing on the cake. It was a really sweet one."