Pep Guardiola's men needed penalties to beat Chelsea in the EFL Cup final and were run extremely close by Liverpool in the Premier League, but Saturday's triumph was a procession as City rounded off an historic campaign in incredible fashion.
Although the first big chance of the game was created by Watford, a dominant City made them pay just before the half-hour with David Silva's first goal since December and Raheem Sterling doubled their advantage with 38 minutes on the clock.
Watford's positive start to the second period was futile and ruthless City swept them away in style, as Jesus set up substitute Kevin De Bruyne and then got in on the act himself.
Sterling rounded off a glorious day for Guardiola's men by completing his hat-trick with two in the last nine minutes.
For all of City's early domination, the first opportunity fell to Watford on the break in the 10th minute. Gerard Deulofeu led the counter down the right and his cross was perfect for Roberto Pereyra but the Argentinian's shot was blocked by the outrushing Ederson.
City capitalised on that let-off 16 minutes later, as Sterling headed the loose ball into the left side of the box and David Silva fired across Heurelho Gomes into the bottom-right corner.
Watford's task became even greater late in the half when Jesus nudged Bernardo Silva's cross past Gomes and Sterling smashed in from inches out.
Gomes was well beaten when City finally extended their lead just past the hour, as Watford were caught on the break by Jesus and he squared to the exceptional De Bruyne, who cleverly sidestepped the goalkeeper and converted six minutes after coming on.
Jesus got the goal his performance deserved in the 68th minute, racing on to De Bruyne's pass and confidently slotting past Gomes.
Sterling completed the rout and his hat-trick in the latter stages, first meeting Bernardo Silva's cross and firing in from close range, before then latching on to De Bruyne's right-wing delivery and finding the net despite Gomes' best efforts, capping a momentous day for City.
City make history yet again
Guardiola's spell in charge of City has been remarkable. Even though supporters will have been disappointed by another failure in the Champions League, winning English football's first ever domestic treble is a fine consolation, particularly given Saturday's astounding victory.
After Pereyra's early chance, there rarely appeared to be much hope for Watford as they became the latest victims of Guardiola's exceptional City, who showed – if anyone had any doubt – they are the leading power in English football.
De Bruyne injects brilliance in stunning cameo
Although Sterling and Jesus deserve plaudits for their respective performances, De Bruyne was truly immense after his 55th-minute introduction for Riyad Mahrez. The Belgian injected drive, creativity and power in midfield, while he got a goal and had a hand in Sterling's hat-trick clincher.
