London: Diego Costa provided the lightning conductor as the longstanding friction between Chelsea and Arsenal crackled to the fore during his side`s ill-tempered 2-0 victory in the Premier League.
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 on Saturday.
"I think his behaviour is unacceptable. If you look at the pictures, what he does to Koscielny, before he pushes him down in the face, he hits him in the face. And he always get away with it.
"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.
"In that day, we lost the game, we lost the cup. It was not good for us. We behave in a fantastic way. No excuses, not crying, not moaning, just Mr Jose Mourinho, my players and Chelsea Football Club.
"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."Asked to justify Costa`s behaviour, Mourinho said that the focus should instead be on Gabriel`s "mistake" in retaliating.
When pressed on Costa`s apparent assault on Koscielny, he attempted a joke, telling his inquisitor: "I can guess that when you were a kid, you were playing badminton."
Costa was hit with a retrospective three-game ban for treading on Liverpool`s Emre Can in a League Cup tie last season and Wenger invited the Football Association to look at his latest indiscretion.
But Mourinho, who left captain John Terry on the bench, said: "I think he said before the game that I have to cope with my defeats. Tonight (Saturday), he has to cope with his defeat."
After Gabriel`s dismissal, Kurt Zouma headed Chelsea in front from a Cesc Fabregas free-kick in the 53rd minute.
Arsenal then lost Santi Cazorla to a second yellow card before Eden Hazard added the coup de grace with a deflected strike a minute from time.
Wenger said it was "frustrating" to have conceded a goal from a set-piece and described Cazorla`s dismissal, in the 78th minute, as "game over".
While Arsenal nurse their wounds after back-to-back defeats, following the mid-week 2-1 loss at Dinamo Zagreb in the Champions League, Chelsea are hopeful of a turnaround.
Mourinho`s men began their Champions League campaign by beating Maccabi Tel Aviv 4-0 and must now seek to whittle away Manchester City`s eight-point advantage in the Premier League.
"In these two matches, we improved a lot, in many aspects," said Mourinho, whose side launch their League Cup defence at Walsall on Wednesday.
"Defensively, the team was much better. The attacking players defended much better than before. They created a compact zone and reacted very well when they lost the ball.
"Sometimes against 10 men, teams play bad. We played very well against 10 men. We gave them no chance."