Chelsea proved Manchester City are not invincible at Etihad Stadium as they inflicted their first home English Premier League defeat of the season with a 1-nil victory.
City have reeled off 11 home league wins out of 11 this season - and another over Jose Mourinho's side would have taken them ahead of Arsenal at the top of the table.
Instead, Mourinho and Chelsea produced a counter-attacking masterclass perfectly designed to take advantage of City's natural attacking instincts, and Branislav Ivanovic's first-half goal gave them a thoroughly deserved win.
It was the first time City had failed to score in a home league match since November 2010 as the Premier League's most potent attack, with 68 goals, was kept out by the best defence - the visitors have conceded just 20.
Arsenal lead with 55 points, Manchester City and Chelsea have 53.