Costa sparked the incident, late in the first half, that culminated in the dismissal of Arsenal centre-back Gabriel, who was goaded into kicking out at the Chelsea striker following a penalty-box scuffle involving Laurent Koscielny.
Costa twice appeared to swing his arm at Koscielny and Arsenal manager Arsene Wenger was exasperated that referee Mike Dean had sent off Gabriel and allowed the Spain international to remain on the pitch.
"He can do what he wants, he stays on. Everybody else who responds to him has to be sent off," a visibly aggravated Wenger told his post-match press conference at Stamford Bridge yesterday.
"I don't understand Mike Dean's decision at all."
Wenger accepted that Gabriel had been wrong to react, but he said that Dean's handling of the incident had shown "weakness" and "naivety".
Chelsea manager Jose Mourinho dismissed Wenger's claims, however, and used the opportunity to lecture his long-time adversary on the importance of "emotional control".
"I played against Arsenal 12, 15, 18 times, I don't know, and only once he (Wenger) didn't moan," said Mourinho, who shared a perfunctory handshake with his opposite number prior to kick-off.
"I played my first derby on the twenty-something of September 2000. Benfica against Porto. And I told my players before the game, to win derbies you need emotional control.
"Without emotional control, forget it, you don't win. It's a basic thing of the game.
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