Guardiola delighted with Grealish's return to form in win over Chelsea
Second-half goals from Riyad Mahrez (31) and Julian Alvarez (22) secured victory for City and took them into the fourth round.
Grealish was City's standout player, orchestrating the Premier League champions' attacks in the absence of Kevin de Bruyne and Phil Foden.
"We spoke many times with him, the first intention is go to score a goal," Guardiola told reporters. "He's not a real threat for the back four because he's going to pass the ball, but today his body language is 'I'm going to score a goal'. Then after, shoot or pass.
"Today, there were three or four times when he did it, and this is what we wanted. Today he didn't score but with the chances, he will do it. He was exceptional again, Jack is playing really, really good."
Midfielder Kalvin Phillips (26), who hopes to make England's squad for the World Cup in Qatar, made his return from shoulder surgery and Guardiola was pleased with his impact.
"Kalvin had a good 40 minutes. He didn't play for a long time, and he played with incredible personality," Guardiola said.
City, who are second behind Arsenal in the league, host Brentford on Saturday.