The former Arsenal midfielder scored twice in Sunday's 3-0 Premier League win over Swansea, continuing his finest run of form in a City shirt.
Having often flattered to deceive under the stewardship of Roberto Mancini, Nasri has blossomed into a key figure following the close-season arrival of Pellegrini, assuming a particularly integral role in light of David Silva's injury lay-off over the past month.
"I think he is happy," said the Chilean manager. "Maybe he feels like now he is again an important player and the way the team plays is very comfortable for him also."
Pellegrini is far from surprised by the quality Nasri has shown this season.
"All of you know that he's a big player," added the 60-year-old.
"Before he was at City I managed against him in the Champions League (when Pellegrini was in charge of Villarreal for a quarter-final against Arsenal) and he's a very, very good player.
"He's again playing in the way he knows how to play."
