Grealish netted inside two minutes and Omar Marmoush added a second goal as City moved into fourth place in the table with 51 points from 30 games. Leicester are in 19th with 17 points from the same number of matches, 12 points from relegation safety.
Pep Guardiola watched from the stands as he serves a touchline ban and what seemed like several thousand City fans missed the first nine minutes, including Grealish’s goal, as they vacated their seats in protest at the club’s ticket prices.
Marcus Rashford scored his first league goal for Aston Villa who earned a comfortable 3-0 win at Brighton & Hove Albion, which moved the visitors ahead of the hosts in the Premier League standings.
Rashford, who joined on loan from Manchester United in February, put them ahead six minutes after the break, having scored twice in their 3-0 FA Cup win over Preston North End on Sunday.
Brighton had a goal overruled for handball before substitute Marco Asensio, another player who arrived on loan at Villa, doubled the lead 12 minutes from time and Donyell Malen wrapped up the win with an added-time goal.
Villa move up to seventh on 48 points, one behind Chelsea who host Tottenham Hotspur on Thursday, while Brighton are one point behind in eighth place.