It was yet another scintillating performance on the road as City also set a new Club record in the process.
Goals from Raheem Sterling and Bernardo gave the champions a two-goal advantage at the break, though it perhaps could and should have been many more.
It was a similar story after the re-start, with Bernardo scoring a sumptuous third to seal victory just past the hour. Phil Foden and Jack Grealish hit the woodwork before Chucho Hernandez pulled one back on 74 minutes.
It was a blistering start by the champions.The home side barely had a touch as City moved the ball around with speed and purpose, stretching Watford from right to left and mercilessly pinning them in and around their own box.
The warning signs had already been posted when Aymeric Laporte saw a free header cleared off the line by Joao Pedro on three minutes, but the respite was brief as City took the lead a minute later.
Phil Foden received the ball on the left and his curling cross into the six-yard box found an unmarked Sterling who expertly nodded down and past Daniel Bachmann to make it 1-0.
Within the next six minutes, Jack Grealish could have scored another two goals. First he arrived unmarked to head a corner point-blank at Bachmann – either side of him would surely given the goalkeeper no chance – and moments later he collected another fine Foden cross but saw his shot beaten away by the Watford No.1.
But if Jack was down about those misses, he didn’t let it affect his game and he was heavily involved in City’s second of the evening.
His ball from the halfway line found Ilkay Gundogan who played a one-two with Bernardo before seeing his shot saved – but Bernardo was first to the loose ball, skipping past two challenges in a blink before beating Bachmann on his near post to make it 2-0.
It was a fifth Premier League goal in eight games for the Portuguese who can do no wrong.Watford improved in the second-half, but City continued to create chances.
On the hour-mark, Foden saw a low shot pushed on to the foot of the post, but four minutes after that, the three points were effectively sealed with more Bernardo brilliance.
On the right of the Hornets’ box, he cut inside before curling a powerful drive into the top left corner – a thing of beauty – and his sixth in eight Premier League games.
The only blot on City’s copybook came on 74 minutes when Chucho Hernandez fired a crisp low drive past Ederson whose wait goes on for his 100th clean sheet in sly blue.