The victory marked our 13th consecutive win over the Hornets and it came thanks to a fantastic all-round display.
Pep Guardiola's men began the game in confident fashion and broke the deadlock in the 31st minute after the lively Raheem Sterling fired the ball into the top corner from 12 yards, following neat build-up play involving Kyle Walker.
Nine minutes later, Sterling made it two, tapping in the rebound after his penalty was saved well by Ben Foster.
Guardiola's side kept up the attacking momentum in the second period and made it three just after the hour mark.
Sterling's shot was parried by Foster and Phil Foden was in the right place at the right time to stroke the ball into the net from close range.
Just a few minutes later, we were celebrating again as Aymeric Laporte rose highest to nod in our fourth, meeting Kevin de Bruyne's accurate free-kick.
See the best images from the victory via the gallery below!