Chelsea preserved its unbeaten start and six-point lead by defeating London rival Tottenham 3-0 thanks to first-half goals in a three-minute span by Eden Hazard and Didier Drogba, followed by a third from substitute Loic Remy.
It was a predictable loss for Spurs, which hasn't won at Stamford Bridge since 1990 — a run that now extends to 28 games.
Sergio Aguero is leading City's attempts to haul back Chelsea, with the Argentina striker taking his league-high tally to 14 goals by scoring in each half in a 4-1 win at Sunderland. The champions had to come from a goal down in the 19th minute, with Stevan Jovetic and Pablo Zabaleta also scoring at the Stadium of Light.
With four straight wins in all competitions, City has clearly overcome an earlier wobble. By scoring 10 goals in its past three games, City looks to be back to the kind of form that swept the team to a second title in three years last season.
"The team is coming again in their performances and all the players are having more trust in what we are doing," said City manager Manuel Pellegrini, who hailed the continued excellence of Aguero.
"At the moment, we are seeing very high performances from him. Not only is he scoring but he's playing well as well."
City opened up a four-point gap on third-place Southampton, which conceded an 89th-minute goal to Sanchez in a 1-0 loss at Arsenal.
The Chile forward has scored 14 goals in 22 games in all competitions in his first season in English football, with his latest strike hauling Arsenal up a place to sixth — three points behind Southampton.
"We were jaded physically but Alexis Sanchez can dig deep and has such desire and a will to win," Arsenal manager Arsene Wenger said. "He still finds that resource to get you something special."
Coming soon after a 3-0 loss to City on Sunday, Southampton's fast start to the season is being derailed and the team could drop out of the Champions League places if it loses to fourth-place Manchester United on Monday.
Everton drew 1-1 at home to Hull in the other game, with Sone Aluko scoring an equalizer for the visitors as they ended a run of four straight losses and climbed out of the relegation zone. Romelu Lukaku gave Everton the lead.
Diego Costa was suspended for Chelsea and his replacement — veteran striker Drogba — made the most of a rare start.
The Ivory Coast great set up Hazard for the opener in the 19th and then scored himself — for the fifth time since his return to Chelsea — after goalkeeper Hugo Lloris' weak clearance was seized on by Hazard and Oscar.
"It's remarkable," Chelsea manager Jose Mourinho said of Drogba. "He's a team player . not selfish, not vain, a humble guy who plays and fights for the team. Fantastic."
Tottenham's feeble defence was breached again in the 73rd when substitute striker Remy sidefooted after brushing off Jan Vertonghen.
Chelsea is undefeated this season in 20 matches and its 23-game unbeaten run in the league and cup equals a club record.