Yet, when Mahrez came off the bench, the Leicester fans made their thoughts crystal clear.
The Foxes have taken just one point from their last four Premier League away games, having been unbeaten in the previous seven.
The move was widely interpreted as Guardiola making a point over rough treatment of his players after Leroy Sane suffered ankle injury against Cardiff, and both Kevin De Bruyne and Brahim Diaz were the victims of reckless challenges in the next game against West Brom.
Aguero punished a awful clearance from Kasper Schmeichel with a sublime dinked finish to net his 12th treble for the hosts, before saving his best until last with a dipping drive that crashed in off the bar. City are interested in bringing him to The Etihad in the summer, but they face competition from Manchester United given their poor defensive options.
DF Kyle Walker, 8 - The full-back's pace was crucial in dealing with Leicester's counter-attacking threat and his energy late in the game opened up the chance for Aguero's hat-trick goal.
The Argentina global has now scored 13 goals in 10 matches since the turn of the year, when City's other main goal-getter Gabriel Jesus was ruled out with injury.
With City thus in complete and utter control of the game it became hard for Leicester to muster any sort of comeback, mainly due to the home side's remarkable ability to keep the ball.
LEICESTER CITY: Schmeichel 5, Dragovic 6, Maguire 6, Fuchs 6, Albrighton 5, Silva 5, Ndidi 5, James 5, Chilwell 5, Diabate 5, Vardy 6. As a result, I think they will leave Manchester with a loss. Palace have lost only two of their previous 15 top-flight games and Hodgson will be hoping to compound matters for his England successor. The Belgian picked up the ball on the right-hand side, slipping the ball through to Aguero, whose fierce shot was too strong for Schmeichel to keep out at the near post.
77' - GOAL! Man City 4-1 Leicester City.
Manager Claude Puel defended his decision to fast-track Mahrez's comeback despite admitting for the first time the player had made a "mistake" by not being available for the club's previous two matches.