City were not at their best at Stamford Bridge but Grealish produced the moment of incisiveness they needed with a slide-rule pass across the face of the six-yard box to hand fellow substitute Riyad Mahrez a tap-in.

Grealish's third Premier League assist of the campaign matched his tally from the entirety of last season, but the ex-Aston Villa star still had more goal involvements (16 - six goals, 10 assists) in his final season in the Midlands than he has had in almost 18 months with City (10 - four goals, six assists).

"When I came here, I'll be honest with you, it was so much more difficult than I thought," Grealish, 27, told Sky Sports after City's 1-0 win moved them to within five points of leaders Arsenal.

"In my head I thought I was going to the team sitting top of the league and I was going to get so many goals and assists and obviously it isn't the case. A lot of teams tend to sit in against us and that wasn't the case at Villa."

Grealish added: "[Ex-Aston Villa manager] Dean Smith would tell me to go and find the weak link in the defence, whether that was on the right, the middle or whether I wanted to hug the touchline - and at Villa, I always had an overlapping full-back.

"I came into City, having been at Villa my whole life, and I've never had to change. I've always been used to that. I didn't realise how hard it is to adapt to a different team and manager."

Grealish and Mahrez had each only been on the pitch for three minutes and 43 seconds before they combined for the crucial goal that cut league leaders Arsenal's advantage.

"We've had games this season - Everton and Brentford recently for example - where they've had a back five and they've sat in against us," Grealish added.

"Against a back four today it just felt so much more open and we were saying we were desperate to come on."

City bench the difference in title race?

Riyad Mahrez's tally of nine top-flight goals off the bench for City is bettered only by Edin Dzeko (13) and Sergio Aguero (12)

Arsenal manager Mikel Arteta introduced just one substitute in Tuesday's frustrating goalless draw at home to Newcastle - and it was easy to understand why, given the lack of attacking options on the Gunners' bench.

By contrast, Guardiola was able to bring on £160m worth of talent on the hour mark at Chelsea and his double switch paid dividends almost immediately.

"Grealish's body language is exceptional if he plays or doesn't play - these type of guys always play good," Guardiola told Sky Sports.

"With Riyad [Mahrez] I knew the space would be there for him. He's good one-on-one in the final third."

Indeed, Mahrez is making a name for himself as a super sub - the Algeria winger is the Premier League's top-scoring substitute since he joined Manchester City in 2018-19.

"It's sort of unfair, isn't it, the Manchester City bench?" former Chelsea striker Chris Sutton observed on BBC Radio 5 Live.

"And will that be the difference this season? With their squad, do they have the edge over Arsenal?

"Grealish has taken a bit of a battering at times - doesn't score enough goals, not enough assists.

"But that was a moment of brilliance for the goal - he knew exactly what he wanted to do and the weight of the ball, not too hard, not too soft, it was just perfect for Mahrez."

Grealish and Mahrez were not alone in making an impact as a replacement - with 18-year-old Rico Lewis producing another assured performance after coming on as a half-time substitute following a ragged first half from Guardiola's side.

"In the first half everything was sloppy, we had no rhythm - but we got better when Rico came in," Guardiola told Match of the Day.

"He has the ability and talent to make our game better. Most of the players play good, but he has the ability to play good but make the others play better.

"As a midfield player that talent is extraordinary."