Nasri capped a fine display with a crucial late strike that handed Mancini's team three points to keep them in touch with league leaders Manchester United.
The Italian manager has now asked Nasri to perform more consistently and believes he can be as important as David Silva has been to City or Xavi is to Barcelona.
"Samir did well but he can do better," Mancini told reporters. "He can improve. He is a top player. If he plays like this he can be like David Silva or Xavi if he plays."
Mancini was also pleased with the return of Carlos Tevez, hailing his "incredible assist" on Nasri's winning goal despite admitting that the Argentine lacks match fitness.
Tevez appeared from the bench to make his first appearance since September, with Mancini insisting that their relationship is fully repaired.
"Carlos is not 100 percent but that is normal," Mancini explained. "But he knows football. That was important because he did an incredible assist for Samir.
"What happened with him finished one month ago when Carlos came back and everything was finished. I have spoken to Carlos every day in the last month.
"He knew he would be on the bench today and would probably play for 20 minutes. If he can find good form in 10 days or two weeks, that would be important for us. Now he needs to play some games, for us, him and his future."
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