|West Brom celebrate after Jerome Thomas scores their third goal to shock Arsenal at the Emirates [GALLO/GETTY]
Champions Chelsea suffered their first defeat of the season when Carlos Tevez scored to give Manchester City a 1-0 win at Eastlands.
The Argentine went on a solo run to slot a shot through defender Ashley Cole's legs and score his fourth goal of the English Premier League season.
Arsenal had the chance to close the gap to one point at the top of the table but fell to a shock 3-2 home defeat to promoted West Bromwich Albion.
West Ham United got themselves off the bottom of the table for the first time this season by beating Tottenham Hotspur 1-0 at Upton Park, while Liverpool drew 2-2 at home to Sunderland to sit 15th in the league.
Tevez's 59th-minute strike, his fourth in three games against Chelsea, ended the Londoners' run of five consecutive league victories and an avalanche of goals.
Defeat would have left Roberto Mancini's expensively assembled team 10 points adrift of Chelsea but they have now cut the gap to four.
Mancini suggested on Friday that Chelsea's title defence would be a stroll, but City stifled a Chelsea attack that had scored 21 goals in a perfect five-match start to the season and in Tevez had a player capable of snatching victory in a match where clear chances were few and far between.
Chelsea manager Carlo Ancelotti was critical of his side's performance and had no complaints about a loss that followed hot on the heels of Wednesday's League Cup defeat by Newcastle.
"We didn't play how we wanted," the Italian told Sky Sports.
"We were not able to use our quality and were too complicated. City performed well in midfield and won a lot of tackles and they deserved to win."
City rarely threatened in the first half with Tevez a peripheral figure.
Chelsea were the more fluent side and went closest before the break when defender Branislav Ivanovic headed against the woodwork and then saw his follow-up effort saved by Joe Hart.
Immediately after the break Nicolas Anelka forced a fine low save by Hart while at the other end David Silva forced a rare save by Petr Cech with a first-time shot from a tight angle.
City's winner came completely out of the blue.
There seemed no danger when Yaya Toure passed to Tevez inside his own half but the Argentine was allowed to run unimpeded towards the Chelsea area before jinking right and lashing a shot through the legs of Ashley Cole and beyond Cech's despairing dive.
It was only the second goal that Chelsea had conceded in the league this season and their response was less than convincing, especially after a disgruntled Didier Drogba was substituted.
Manchester United can close to within a point of Chelsea with victory at Bolton Wanderers on Sunday. City are in fourth place, four points adrift.