Cahill and Zouma played in Chelsea's 4-2 defeat to Bradford City last weekend, but the England international lost his place while the Frenchman started alongside John Terry for their League Cup semi.
Zouma was forced to use his pace when Sterling broke away 16 minutes into the first half, tracking down the 20-year-old and dispossessing him in the box.
And Mourinho insisted before kick off this is what he had in mind for his centre-half.
"He's very fast. He's the fastest defender we have and Liverpool normally play on the counter-attack with fast players to get in behind," Mourinho told Sky Sports.
"We believe in spite of him being a young kid and this being the first time he plays in the semi-final of a cup, we believe that his evolution has been good in the Capital One Cup.
"We don't deny that we try to reach the final and win the competition but sometimes there is a space for the improvement of young players and Zouma is an important young player for us."
Tag : Football News