After conceding eight goals in their first six Premier League matches, City have only let in two in the past six games, giving a sturdy base to a side that has now gone ahead of their leaky rivals.
For all the wonderful attacking players in evidence in the squads of the Premier League's three best sides, it is Manchester City's recently refound defensive solidity that has moved them to the top of the league.
Last season Vincent Kompany spearheaded the league's best defensive unit, and City's recent run has now moved them joint top of the defensive rankings for this year's league.
The criticism that surrounded Roberto Mancini after the first few games related to a string of what seemed like unnecessary changes to a defensive group that had performed so well last season.
Mid-game changes from a back four to a back three were derided as City's back line looked open to all comers, especially in Europe. Those defensive issues look to have ensured they will fail to qualify from the group stage of the Champions League for second successive year, but Mancini appears to once again have a hold on how to keep a clean sheet in the league.
After an opening spell of six games were City conceded eight goals, with no clean sheets, Mancini's side have produced four clean sheets in the last six matches, conceding only two goals. As Chelsea and Manchester United's defensive issues have started to cost them points, City have tightened up and overtaken their rivals.
Of the three sides at the top of the league, it is surely Manchester City who teams now fear playing the most. They are unbeaten this season, have the best defence of the three, and now have Silva, Tevez and Aguero back fit and starting matches in their attack.
When going into games against Chelsea and Manchester United, teams know they have a chance to get a goal, and that a strong defensive performance could yield one or three points.
That confidence isn't there when playing City, especially when visiting the Etihad, where they have not lost for 36 matches. In contrast Chelsea and Manchester United have both already lost at home this season.
The Premier League seems to be more attacking than ever this season, with many sides playing attractive football in top heavy formations.
Manchester City are clearly one of those sides, with perhaps the best group of attacking players in the league.
But it is their defensive solidity that has put them top of the pile for the moment, and unless Manchester United and Chelsea follow their lead in tightening up, they could well stay there.