Diego Costa had missed 10 games in his first two Chelsea campaigns through suspensions but has not picked up a booking since September's defeat to Arsenal.
The Spain striker took his goal tally to 11 in Saturday's 3-1 win over Manchester City, which extended Chelsea's winning streak to eight Premier League matches.
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Gary Cahill praises Diego Costa form
And Cahill believes the 28-year-old has matured at Stamford Bridge his term and shrugged off his reputation as a controversial striker.
“I think we are seeing more composure from Diego this season,” Cahill said. “I know everyone thinks he is an angry guy but you can see a smarter player now.
“We were starved of the ball in the first half and so was he, and in the last few years maybe he gets frustrated at that.
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Diego Costa guided Chelsea to a comeback win over Manchester City
“But this time he kept his cool and got more involved in the second half and when he does that he is one of the best going.
“He has been fantastic this season, showing maturity and still banging the goals in. He’s on fire at the minute and I hope it continues.”
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