"It was strange because nobody could see it coming.
"I think at the time Chelsea were third in the league and to get beaten like that, I just don't know how it happened because they only had six chances and we were unlucky.
"We'll have to give them a run for their money, work as hard as we can and hopefully we can get a result.
"Even a draw would lift confidence."
Johnson admitted City boss Sven Goran Eriksson was angry after last weekend's 3-1 defeat at Birmingham.
He added: "We know when he's not happy but he's a really good manager and he tells us when we're good and he tell us when we're bad.
"It's imperative that you do well in every game because if you don't then he can just go out and buy someone else."