The center of midfield and center of defense has been great for Manchester City, but despite being the much better team for the opening 30 minutes of the Manchester Derby, they trail Manchester United at halftime. Nani, despite being a major focus of Roberto Mancini's tactics, has been United's best attacking threat and was the man who scored the goal to put United up 1-0. Zabaleta was left in the dust on the goal, and it wasn't the first or last time he looked vulnerable. He's been an obvious weak link in City's defense.
Since we're already on the Negative Nancy train, we might as well discuss the other players who are failing to make a positive impact. Carlos Tevez hasn't been "bad," per se, but he hasn't made his normal impact. City have relied on him to do a lot this season, and average won't do, especially if Edin Dzeko isn't in the team. More "poor" than "average" has been James Milner, who is basically invisible. He's done nothing going forward and he's allowed Ryan Giggs and Patrice Evra to have a more significant impact on the game than they should. United have been effective attacking down their left, which Milner is supposedly supposed to minimize.
That's the bad, but despite the negatives and the scoreline, there have been a lot of good things about Manchester City. Micah Richards has been great at right back while David Silva has had a serious impact on the game. He had a bad miss in the 6th minute, but other than that, he's been superb.