“Every time you give him the ball, you feel like something’s happening,” said defender Ake, who benefited from Grealish’s handiwork by heading in the opening goal from one of his corners.
“He always wants to take players on, he always wants to create something. With the players we have in the team already and with him, you can see we can create so many chances and score goals.
“He’s a big plus and bonus for us.”
With Kevin De Bruyne also starting his first game of the season, City were formidable going forward as they began their 11th successive Champions League campaign in fine fashion.
The result also gave them an early lead in Group A as chief rivals Paris Saint-Germain were held to an unexpected draw by Club Brugge.
City, last season’s runners-up, face the star-studded French side – beaten finalists in 2020 – in their next European outing in a fortnight.
Defensively, however, City were exposed at times. The game was an open affair and French midfielder Christopher Nkunku enhanced his reputation with a well-taken hat-trick in a losing cause.
Ake said: “First of all we were happy that we won the game – it was a difficult game – but on the other hand we conceded three goals and that’s something we have to look at.
“It’s never good to do that, especially at home. I think we were sometimes a little bit sloppy.”
City always held the upper hand after Ake put them ahead in the 16th minute and Nordi Mukiele headed into his own net, but Nkunku’s regular replies meant they had to keep pushing.
Nkunku made it 2-1 and then struck again after first a Riyad Mahrez penalty and then after Grealish’s superb curling effort.
Joao Cancelo put City two goals ahead for a fourth time and this time Leipzig could not respond. Their hopes ended when former City defender Angelino was sent off and Gabriel Jesus wrapped up the scoring late on.
City host Southampton on Saturday and travel to Chelsea the following week but the build-up to their eagerly-anticipated trip to the Parc des Princes, where they famously won last season, will soon begin.
“Obviously it’s going to be a big one,” said centre-back Ake, who played alongside Ruben Dias with both John Stones and Aymeric Laporte out injured. “That’s why it’s good to start this game with a win so we can go into that with a bit of confidence.”
Asked how he would prepare to face the likes of Lionel Messi and Neymar, the 26-year-old said: “You have to be prepared, they have top-quality players. We’ll train on that and watch clips together and see what we can do as a team.”