Nasri was at fault for United’s late winner as he turned away from Robin van Persie’s free-kick and deflected it past Joe Hart.
That left City trailing United in the league by six points. But boss Roberto Mancini insists his champions are still the best despite losing 3-2 to their rivals.
He said: “I don’t say they are lucky because United are a strong team.
“Three years ago they were better than us but now they are not better than us.
“I don’t think it’s a big problem to recover six points.”