Kurt Zouma and Eden Hazard gave Chelsea a controversial 2-0 win over nine-man Arsenal yesterday while leaders Manchester City crashed to a shock 2-1 defeat against West Ham.
The acrimonious relationship between Chelsea manager Jose Mourinho and Arsenal boss Arsene Wenger seeped through to both teams at Stamford Bridge in a tetchy London derby featuring even more flashpoints than usual.
And at Eastlands, Kevin de Bruyne's first goal for City wasn't enough to salvage their 100 percent start against the Hammers, who have defeated Arsenal, Liverpool and Manuel Pellegrini's side in their first three away games this season.
City fell behind in the sixth minute when on-loan Chelsea winger Victor Moses fired home from 20 yards for the first league goal conceded by Pellegrini's club this term.
Senegal forward Diafra Sakho netted the visitors' second from close-range in the 31st minute.
Belgium midfielder De Bruyne, a £55 million ($85 million, 75 million euros) signing from Wolfsburg last month, marked his first City start with a clinical finish in first half stoppage-time.
But a brilliant Adrian save from Nicolas Otamendi's header ended the hosts' winning run at five matches and lifted West Ham into second place.
"We played very well in the second half, though not in the first. We were not the aggressive team we need to be at home," Pellegrini said.
"We knew this would be a difficult game because it was not luck that they beat Liverpool and Arsenal."
At Stamford Bridge, Wenger was furious Mike Dean opted not to send off Diego Costa following a clash with Laurent Koscielny and the referee further infuriated the Frenchman when he dismissed Gabriel for kicking Costa and then showed Santi Cazorla a red card in the second half.
"I would not like to be Mike Dean tonight. Costa twice should be sent off," Wenger said.
"In every game Costa has aggravation and he gets away with it because of the weakness of the referee."
Mourinho's response felt designed to provoke Wenger as he said: "I don't have a view on the sending off. Man of the match for sure was Diego Costa. He brought everything to the game."
Chelsea striker Costa was booked for shoving over Koscielny after whacking the Arsenal defender in the face moments earlier.
Gunners defender Gabriel remonstrated with Costa and was booked for his complaints.
But the Brazilian couldn't keep his emotions under control and in first-half stoppage-time he aimed a sly kick at Costa right in front of the referee, who immediately brandished a red card.
Chelsea made their numerical advantage count in the 53rd minute when French defender Zouma was left unmarked to head in a Cesc Fabregas free-kick.
Cazorla was sent off in the 79th minute when the Spanish midfielder caught Fabregas with an ugly lunging tackle.
Belgium midfielder Hazard guaranteed the champions' second league victory of the season in the 90th minute when his strike deflected off Calum Chambers to leave the Gunners without a league success against the Blues since 2011.
