Manchester City beat Chelsea last season, too. Home and away and scored six goals. It did not make a blind bit of difference. City won the home fixture 2-1 on December 5, 2009 then drew at Bolton Wanderers and lost at Tottenham Hotspur. On February 27, 2010 they won 4-2 at Stamford Bridge, but the next three games included a draw with Sunderland and defeat by Everton.
By contrast, Chelsea's reaction to the first City defeat was to stay unbeaten in all competitions until February 10, and their reaction to the second was to drop two points in the Premier League between then and the game at Eastlands on Saturday. That is how titles are won.