The prolific Argentinian came to City's rescue to ensure they avoided an FA Cup shock against Watford with a second-half hat-trick.
City remarkably trailed 2-0 to the Sky Bet Championship side at half-time of their fourth-round tie at the Etihad Stadium, but it was a different story after the break.
A team reshuffle laid the foundations for Aguero to level the scores with a double.
City did not go ahead until luckless Hornets goalkeeper Jonathan Bond allowed an Aleksandar Kolarov shot to slip through his grasp three minutes from time but Aguero quickly added a fourth.
That took his tally for the season to 25, six of which have come in four appearances since he returned from a month-long injury absence.
The 25-year-old said: "The important thing is the goals contribute to the team's victory, the team wins and we win titles.
"I don't have any specific goals to reach - but as many as possible.
"We weren't expecting to score four goals. We knew at half-time we needed to improve and in the end we won and we have made it to the next round. We are happy with that."
City were lethargic in the first half and that was ruthlessly exploited by a fired-up Watford side playing well above a standard that might be expected of a team 15th in their division.
They claimed a deserved lead when Troy Deeney set up Fernando Forestieri - the only player in the Watford side to have commanded a transfer fee, £500,000 - after 21 minutes.
The impressive Deeney doubled the lead on the half-hour after some slack defending by City.
City boss Manuel Pellegrini later branded his side's defending a "disaster" and said he could have made 11 substitutions at half-time.
The changes he did make however, sending on Vincent Kompany and Pablo Zabaleta, brought more organisation at the back and changed the game.
Aguero said: "In the first half they played really well and put a lot of pressure on us but in the second half we made fewer mistakes and we were able to get the goals. It is good we were able to come back."
City's third substitution saw striker Stevan Jovetic sent on up front to link with Aguero and Edin Dzeko.
The Montenegro international has endured a torrid time since joining City in a £22million move from Fiorentina last summer due to a succession of injuries and illness.
He did not get on the scoresheet but did combine well with the two strikers and could have a key role to play in the closing stages of the season as the fixtures mount.
Jovetic has so far been the odd man out among the strikers with Negredo having also scored 23 times and Dzeko 16.
The 24-year-old told City TV: "I am so happy for them. I play with them and I need to say thank you to them because we are playing so well and we are where we are in the table.
"From now I want to score also and get close to them.
"We have a lot of games and I hope I get my chance and I will play.
"Everything is going well, I'm very happy to be back on the pitch and to be able to help the guys."
Watford and their manager Beppe Sannino left Manchester with much credit.
Although the result extended their indifferent run to just two wins in 17 games, the performance gave renewed hope they could push for a place in the play-offs.
City had not been troubled so much at home since they were thrashed by European champions Bayern Munich in October.
Midfielder Sean Murray said: "That shows how well we have been working this week and what the new manager expects of us.
"The players are giving it back to him. It was a really good feeling being in front, but at the end of the day we lost the game and the second half wasn't as good as we wanted it to be.
"Their quality just showed overall, but I think we can move on and take positives and work on negatives.
"Hopefully when we go back to the Championship we will take positives into the game against Nottingham Forest."