The Englishman scored one wonderful goal and assisted another under the lights at the Etihad Stadium.
City made the perfect start through Nathan Ake, who headed in Grealish's curling corner, before Nordi Mukiele's own goal made it two.
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Riyad Mahrez, Grealish, Joao Cancelo and Gabriel Jesus netted City's remaining goals, whilst Christopher Nkunku bagged a hat-trick for the visitors in a spectacular Champions League clash.
City's summer-signing admitted that this is a performance he has been dreaming of for some time.
"I loved it, I’ve been waiting a while, the past few days and weeks I couldn't wait for this game," he said. "It's a great night! It was one of those games, it had absolutely everything.
"We’re delighted to get the win against a good team, they were full of energy. I’m delighted personally mainly with the three points, but also with the goal and assist.
"Ruben [Dias] went into a tackle, then the ball came to me. When I’m running into the opposition area I back myself against anyone one on one and luckily it paid off and I hit the back of the net. I’m delighted to get the goal."
"Anything can happen in the Champions League, that's why it's such a wonderful competition.
"As soon as the game kicked off I thought in my head i’ve actually played in the competition now. The game and result topped it all off."
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The 26-year-old was an incessant threat on the left flank and was in constant dialogue with manager Pep Guardiola.
Grealish admitted that Guardiola is always providing tips from the sideline.
"The manager was just talking about defensive work," said Grealish when quizzed about his talks with the Spaniard.
"That’s what he’s like, he’s always wanting more defensively and offensively, he’s someone I'm going to listen to after everything he has achieved in the game. He’s always giving out useful information."