Chelsea are guaranteed a healthy away following, having already sold out of their initial allocation and been granted 1,600 more tickets, with Rovers looking for their fans to respond.
Williams said: "The atmosphere at Ewood Park has had a big part to play in our home form. The players and the manager have commented on it.
"We are looking for the same now to help us take a big step towards Wembley. Chelsea are a very good team, we know that, but we believe we can be a match for anyone at home.
"Let's make Wednesday night a night to remember. Chelsea will have a good following but it would be fantastic if we could reproduce the big game atmosphere we have had in the league."