That’s according to Sky Sports pundit Stuart Pearce.
Antonio Conte’s Blues have already lost two games at home this campaign, dropping as many points at Stamford Bridge as they did in the whole of last season.
Pep Guardiola’s men beat Chelsea in west London on Saturday evening to leave the Blues six points behind City and United at the top of the Premier League.
And Pearce reckons the Manchester clubs and Tottenham are taking their chance to shine while Chelsea are struggling.
"You would probably say this was a defining game this weekend," Pearce told Sky Sports.
"To be beaten by a main rival on your own pitch was a denting blow for them.
"I would say you’re looking at probably six or seven (out of 10) at best at the moment.
"The other two, the two Manchester clubs, and Harry Kane at Tottenham, have really put markers down and said ‘look, we’re going to be serious contenders this year’.”
United are back in action after the international break when Jose Mourinho's men travel to Liverpool.
City, on the other hand, host Stoke, while Chelsea travel to Crystal Palace.
