Goals from Michu and Nathan Dyer early in each half sealed a one-sided win for Michael Laudrup's team in south London.
"It was a big week for the club and I think we performed really well," said defender Williams.
"I think it was a brilliant performance from us. It's what we wanted.
"If I could be a little bit critical it's that we could have scored more goals and try to kill the game a little bit earlier."