Match ends, Watford 0, Manchester City 6.
Sergio Aguero scored a hat-trick as Manchester City moved top of the table and handed Watford their heaviest ever top-flight defeat.
Previously unbeaten Watford could have also topped the Premier League with a win against Pep Guardiola's side, but they were undone by City's prolific attack who have now scored 15 goals in three matches.
Aguero headed home a Kevin de Bruyne free-kick before tapping in from close range four minutes later, after brilliant build-up play from Gabriel Jesus and a final pass from David Silva.
Jesus added a third before half-time - his fifth of the season - when he drilled home from Aguero's cut-back, despite tame calls for offside from the Hornets defence.
Watford had kept three clean sheets this season, and came out reinvigorated after half-time, with Andre Carrillo and Richarlison both having decent chances.
But City continued to push forward and added three more.
Nicolas Otamendi headed in David Silva's corner before Aguero completed his hat-trick when he poked home after a pulsating solo run into the box.
Raheem Sterling completed the rout from the penalty spot, after he was brought down by Christian Kabasele.
'It was so good. We are so happy'
Talks of a hangover from a midweek 4-0 win at Feyenoord in the Champions League were quickly put to bed when Manchester City got started at Vicarage Road.
Guardiola's side controlled possession throughout, and returned from the half-time break wanting more even after taking a 3-0 first-half lead.
"It was so good. Especially after an away game in the Champions League. The way we played as a team, we are so happy," said the City boss.
"I was lucky to manage Barcelona with many outstanding performances but this week has been a lot of goals. We have found our game, we can make short passes and we have a lot of energy from our full-backs."
City had 28 shots in total with 10 on target - five in each half - while individually, David Silva had 88 touches, completing 93% of his passes with two assists, and De Bruyne also impressed making four key passes and setting up the opener.
But Aguero was the one man who impressed the most.
Aguero closes in on all-time City record
Aguero was in uncompromising form in front of goal once again, and he has now scored nine goals in five games against the Hornets.
Guardiola particularly enjoyed the 29-year-old's third goal, where he received the ball from Kyle Walker, ran past several yellow shirts and maintained his composure to sneak the ball home from an acute angle.
"His numbers speak for themselves," said Guardiola. "I'm so happy for the third goal because he's so clever in the box. He's able to score a goal at any point."
Aguero's hat-trick - his sixth in the Premier League and 10th for City - has moved the Argentine only two away from Manchester City's all-time scoring record of 177, set by Eric Brook between 1928 and 1940.
Silva brought down to earth with a bang
Marco Silva had made a good start to life as Watford manager, with two wins and two draws from their opening four league matches.
But City provided the Hornets with their first real test from a title contender and they buckled under the pressure.
Despite being under the cosh for the first half an hour, Watford were able to break forward on the counter-attack and Richarlison had the best chance to head home before City went on the rampage.
Silva felt aggrieved that the offside flag was not raised for Aguero's opener and Jesus's goal in the first half, although the decisions were not wildly contested by the players on the field.
They also had a penalty shout when Walker clumsily clattered into Nathaniel Chalobah.
The Hornets did not play badly, but City were just too good.
Man of the match - Sergio Aguero
Man City love a trip to Vicarage Road
- Man City (11) have scored more goals in their last two Premier League games at Vicarage Road than Watford (10) have in their last nine at the ground.
- Gabriel Jesus has been directly involved in 15 goals in his 15 Premier League appearances (11 goals, 4 assists).
- Sergio Aguero scored his sixth Premier League hat-trick; only Alan Shearer (11), Robbie Fowler (9), Michael Owen and Thierry Henry (8) have scored more.
- Aguero has been involved in 11 goals in five appearances against Watford in all competitions (nine goals, two assists).
- David Silva provided two assists in a Premier League game for the first time since March 2016 versus Aston Villa.
Watford boss Marco Silva: "The first and third goals are offside, it is not a normal game. We had a clear penalty for Chalobah. Everything is difficult for us this afternoon.
"City deserved the three points, we learn as a team. We can't make mistakes. But it's really difficult with these decisions."
Manchester City forward Raheem Sterling: "Everyone's buzzing, it was a great performance. We were really clinical and that's what the manager wants from us.
"We have shown signs of great football but we need to be clinical and in the last few games that's what has happened. I'm always pleased to score.
"Give Sergio Aguero a chance and nine times out of 10 he'll score."
Who's up next
Watford travel to Swansea on Saturday in the Premier League (15:00 BST) while Manchester City face West Brom in the EFL Cup on Wednesday (20:00 BST)
- 25HolebasBooked at 29mins
- 16DoucouréBooked at 40mins
- 14ChalobahSubstituted forCapoueat 70'minutes
- 8CleverleySubstituted forPereyraat 64'minutes
- 18GraySubstituted forDeeneyat 74'minutes
- 17De BruyneSubstituted forGündoganat 66'minutes
- 21SilvaSubstituted forSanéat 78'minutes
- 33Gabriel JesusSubstituted forBernardo Silvaat 65'minutes
- 20Bernardo Silva
- Anthony Taylor
- Shots on Target
Second Half ends, Watford 0, Manchester City 6.
Foul by Raheem Sterling (Manchester City).
José Holebas (Watford) wins a free kick in the defensive half.
Attempt saved. Sergio Agüero (Manchester City) right footed shot from outside the box is saved in the top right corner. Assisted by Raheem Sterling.
Attempt blocked. Ilkay Gündogan (Manchester City) right footed shot from outside the box is blocked. Assisted by Benjamin Mendy.
Foul by John Stones (Manchester City).
Troy Deeney (Watford) wins a free kick in the attacking half.
Goal! Watford 0, Manchester City 6. Raheem Sterling (Manchester City) converts the penalty with a right footed shot to the top left corner.
Penalty Manchester City. Raheem Sterling draws a foul in the penalty area.
Penalty conceded by Christian Kabasele (Watford) after a foul in the penalty area.
Attempt missed. Raheem Sterling (Manchester City) left footed shot from outside the box is close, but misses to the right. Assisted by Bernardo Silva.
Leroy Sané (Manchester City) wins a free kick on the right wing.
Foul by Richarlison (Watford).
Attempt blocked. Leroy Sané (Manchester City) left footed shot from the centre of the box is blocked.
Goal! Watford 0, Manchester City 5. Sergio Agüero (Manchester City) right footed shot from a difficult angle on the right to the bottom left corner. Assisted by Kyle Walker.
Attempt missed. Leroy Sané (Manchester City) left footed shot from the left side of the box is close, but misses to the left. Assisted by Ilkay Gündogan.
Corner, Manchester City. Conceded by Daryl Janmaat.
Substitution, Manchester City. Leroy Sané replaces David Silva.
Delay over. They are ready to continue.