The Premier League leaders will need to get a result at Anfield tonight following the Reds' 1-0 win at the Etihad Stadium a fortnight ago.
"It's a tricky one for [Liverpool]," said Johnson. "Do they try to attack us or try to defend against our quality players for 90 minutes? The thing is no matter who we play, we will create chances at some point. We beat them 3-0 at home, so we can score against them.
"No-one is expecting us to go through so the pressure is off for once and we can go there with freedom, play our football and have a go. It won't be easy but we are quietly confident."
The winner of tonight's contest will face Cardiff City in the final after they defeated Crystal Palace on penalties yesterday.