West Bromwich Albion inflicted further misery on Manchester United, winning 2-1 at Old Trafford on Saturday to condemn the champions to their worst start to a Premier League season and leave them in the bottom half of the table after six games.
Morgan Amalfitano and Saido Berahino scored for the visitors either side of a Wayne Rooney leveller to leave United in 12th place in the table a week after they suffered a crushing defeat to local rivals Manchester City.
City also suffered a surprise defeat at Aston Villa, who scored three second-half goals to win 3-2 at Villa Park, leaving Tottenham Hotspur top of the table after a 1-1 draw with Chelsea earlier on Saturday.
John Terry headed a second-half equaliser for Chelsea as the managerial battle between Jose Mourinho and his former apprentice Andre Villas-Boas ended in stalemate.
Southampton's watertight defence held firm as they climbed to fourth with a 2-0 win at home to Crystal Palace, Hull City won 1-0 against West Ham United and Cardiff City won 2-1 away at struggling Fulham.
Arsenal can return to the summit if they beat Swansea City in Saturday's late kickoff.