The strike came on the 25th anniversary of Keelan's passing, adding a poignant layer to an otherwise routine win for the Citizens.
Grealish, shifted inside from his usual left-wing role, wasted no time, scoring just two minutes into the match. Jeremy Doku won possession in midfield and fed Savinho, whose pinpoint cross allowed Grealish to guide the ball into the bottom corner.
The 29-year-old later took to social media, posting, "With me always, especially this day. That was for you, Keelan." Keelan was only nine months old when he passed away in April 2000, a loss that has stayed with Grealish and his family ever since.
City boss Pep Guardiola praised the midfielder's character after the game. "Jack is an incredible human being," he said. "I didn't know (about the anniversary). I can't imagine how tough it can be for mum and dad, his sister, and all the family. It's good that this day he remembers him. I'm pretty sure they remember every single day. He scored a goal and had a good game."
Guardiola also highlighted Grealish's versatility, adding, "He likes to play in the middle. He's comfortable between the lines and has ability. I'm happy for him, especially after a tough season with injuries."
The hosts doubled their lead on the half-hour mark through Omar Marmoush, standing in for the injured Erling Haaland. The Egyptian pounced on a mistake by Leicester goalkeeper Mads Hermansen, smashing the ball off the bar and in for his fifth first-half goal since arriving from Eintracht Frankfurt.
Leicester's only chance came through Bilal El Khannouss, who dragged a shot wide, a miss that summed up their night.
City's dominance continued, though they couldn't find a third goal despite chances, with Marmoush firing over in the second half. The win marked their 13th straight Premier League victory over newly-promoted teams and lifted them into the top four, while also seeing young star Oscar Bobb return from injury.
Guardiola reflected on the result, saying, "The three points are what matter. We've had a tough run, so this is a step forward."
For Leicester, the defeat stretched their losing streak to seven top-flight games without a goal, a grim statistic that leaves them 12 points from safety with eight matches left.
Manager Ruud van Nistelrooy remained defiant, stating, "The most important thing is I stay at it and be the best manager I can be in this situation. It's an extremely difficult moment, but I expect myself to react in a good way."
Leicester, meanwhile, face a daunting fight to avoid the drop as their season unravels.