Jesus stole the show at the Etihad Stadium with the first Premier League haul of three or more goals in his career.
The forward had netted only once in the league since September, but he tore Watford to shreds with a predatory display of finishing.
He struck twice in the first half before Watford's Hassane Kamara briefly reduced the deficit.
Rodri restored City's two-goal advantage and Jesus bagged two more after halftime to complete the rout.
"It's amazing. Sometimes you play so good and don't score and sometimes it is like this and you score all the chances you have," Jesus said.
"I'm happy it was my day. Now is the best moment of the season. When you decide the games and win the trophies. That's what football is for us."
After losing to Liverpool in the FA Cup semifinals last weekend, Guardiola's side have signalled their determination to retain the title.
They dismissed Brighton 3-0 on Wednesday and their demolition of second bottom Watford keeps the pressure on second placed Liverpool.
Jurgen Klopp's men can close the gap back to one point if they beat struggling Everton in the Merseyside derby at Anfield on Sunday.
In a thrilling title race that looks destined to go down to the wire, City have five league games left as they chase a fourth English crown in five years.
Their stroll against Watford was the ideal preparation for the Champions League semifinal first leg against Real Madrid in Manchester on Tuesday.
"If there's one person who deserves the best in life, it's Gabriel. It doesn't matter what position he plays, we know how he fights for his mates. He's fantastic," Guardiola said.
"We had a 'final' today and we won it. Now we have an opportunity to play a 'final' against Leeds.
"Nothing changes. We have to win all five games to be champions."
Guardiola made six changes from the Brighton game, with Ruben Dias replacing the injured John Stones for his first start since March 1 after a hamstring injury.