Chelsea defender Gary Cahill says Diego Costa is mentally transformed this season.

Costa was key for the Blues as they came from behind to beat Manchester City 3-1 at the Etihad on Saturday.

"I've seen more composure from him," said Cahill.

"I know everyone says he's an angry guy, but I'm seeing that composure now.

"I'm sure if you asked him, the first-half didn't go ideally. We were starved of the ball and so was he. He was scrapping around and not getting opportunities.

"In the last few years, maybe he gets frustrated at that point. But he kept his cool and got more involved in the second half.

"The players around him were playing well, defending for our lives when we didn't have the ball and he'll see that."