Within three minutes, Grealish sent in a pinpoint cross for Mahrez to win the match for City.
The victory at Stamford Bridge, against an injury-hit and out-of-form Chelsea, moved City to within five points of Arsenal who failed to pierce Newcastle United’s defence on Tuesday in a 0-0 draw at the Emirates Stadium.
While Arsenal have put their faith in the relatively inexperienced Eddie Nketiah as the man to replace injured striker Gabriel Jesus, City can count on Argentine World Cup winner Julian Alvarez should they need a back-up for goal machine Erling Haaland.
Despite the array of top-name stars at his disposal, Guardiola heaped most praise on 18-year-old Rico Lewis who came off the bench at half-time to replace wing back Joao Cancelo and helped turn the game in City’s favour.
“This young boy has the ability and quality to not just play good, but to make his mates better. This is so difficult to find,” the Spaniard said. “Right now, he is fundamental for us.”
Chelsea coach Graham Potter, whose early unbeaten run in charge of the Blues seems a distant memory after picking up only six of the last 24 points available, was left to rue the injuries that have added to his challenge at Stamford Bridge.
England midfielder Mason Mount was a surprise omission from the squad after picking up a training-ground knock and within the first 22 minutes, Raheem Sterling and Christian Pulisic were withdrawn due to injuries.
Also unavailable on Thursday were a string of players including wing back Reece James, defender Wesley Fofana and midfield anchor N’Golo Kante.
“I’ve never experienced anything like it,” Potter said. “We want … a fully-fit squad and to be able to compete… It’s frustrating for everybody at the moment.”
He said Mount might be available to face Manchester City on Sunday in the FA Cup and hoped Pulisic’s injury was not too serious.