Chelsea, who had won one of their opening five league matches, beat Arsenal 2-0 at Stamford Bridge in a feisty London derby that saw Arsenal finish with nine men after Gabriel and Santi Cazorla were sent off.
West Ham won 2-1 at the Etihad to become the first team not only to beat City in the league but also to score against them this season and have now won at Arsenal, Liverpool and City in their first six matches.
West Ham Coach Slaven Bilic told the BBC: “There will be ups and downs here at West Ham — this result is a major surprise and nine points from the first three away games sounds like a dream, not a plan. But there’s nothing wrong with a dream.”
Any dreams Arsenal may have had of winning at Chelsea for the first time for four years were ended when Kurt Zouma, 20, who replaced dropped 34-year-old skipper John Terry, headed Chelsea ahead after 53 minutes with his first goal for the club.
Eden Hazard then scored his first of the season to make it 2-0 in stoppage time.
City, playing in the day’s late game, had a chance to maintain their 11-point lead over the champions, but West Ham had other ideas and ended City’s run of five straight wins since the start of the season with their shock win.
It also ended a City club record run of 11 straight league wins that started with a victory over West Ham last April.
The Hammers, who have now won at Arsenal, Liverpool and City in their opening six matches, became the first team to score in the league against City this season when Victor Moses fired in a 20-metre drive after six minutes and they doubled their lead when Diafra Sakho scrambled home after 31 minutes.
City, who were beaten 2-1 at home by Juventus in the Champions League on Tuesday, hit back just before halftime when Kevin de Bruyne, who joined City for 55 million pounds ($85.44 million) from Wolfsburg last month, scored his first goal for the club on his first start.
Although City laid siege to the West Ham goal for almost the entire second half and had over 27 goal attempts, West Ham survived for their first away win at City since April 2003.
City still top the table with 15 points, with West Ham and Leicester City on 12, and Manchester United and Arsenal on 10. Chelsea are 13th with seven.
Bilic told Sky Sports: “We deserved it for the way we played in the first half and the way we were fighting in the second half, but this was a different game to the ones at the Emirates or Anfield. This was much harder.”
City boss Manuel Pellegrini, whose team lost for the second time at home in five days, said, “This is football. You need to score to win.
“We let in two easy goals and we must be more concentrated. We had so many attempts but did not score. We were too rushed in the second half but when you go two goals down you play like that.”
Chelsea halted their nosedive down the table when they beat Arsenal in an earlier match that centred on an incident in the first half when Chelsea striker Diego Costa raised his hands to Arsenal defender Laurent Koscielny.
Referee Mike Dean allowed Costa to stay on the field, but Gabriel went for kicking out at Costa a minute later.
Cazorla then saw red for a late challenge on his Spain team mate Cesc Fabregas in the 79th minute.
Arsenal manager Arsene Wenger was angry about how Dean handled matters.
“I think it’s unacceptable what (Costa) does to Koscielny. He pushes him down, he hits him in the face. I do not understand Mike Dean’s decision at all,” Wenger said.
“Why does Diego Costa stay on the pitch and Gabriel is sent off? He will do the same next week and it’s always the same, he is always provoking.”
In the day’s other games Leicester, who were second at the start of the day, slipped back to third after drawing 2-2 at Stoke City although they preserved their unbeaten record after trailing 2-0 at one stage.
West Bromwich Albion beat Aston Villa 1-0, Bournemouth beat Sunderland 2-0, Watford beat Newcastle United 2-1 and Swansea drew 0-0 with Everton.
($1 = 0.6437 pounds)
(Editing by Alan Baldwin)