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Match of the Day commentator
This has echoes of Pep Guardiola's days in charge of Barcelona, when his team containing the likes of Lionel Messi would regularly put five or six past teams in the lower half of the table. Except Watford aren't in the lower half. This is a real statement from City.
A remarkable attacking display from Manchester City. Wow.
Sergio Aguero just doesn't tire.
He has another chance from distance and he stings the palms of keeper Heurelho Gomes.
Raheem Sterling absolutely nails that into the back of the net.
When do we go to brackets? SIX.
Just when you think it couldn't get any worse, Manchester City earn a penalty.
Raheem Sterling is bundled over by Christian Kabasele.
Former Arsenal defender on Final Score
Manchester City play with such energy. The last goal Aguero scored was just unbelievable. He had half the team running after him and he was still able to score.
Pep Guardiola has got them firing today. It's very difficult to get into that side now.
Raheem Sterling has a go with his left foot from just outside the box but it falls just wide of the right post.
The City forward thinks it came off a yellow shirt, but the referee awards a goal kick.
BBC Radio Oxford Presenter at Vicarage Road
It has been another devastating Premier League performance from City. All the damage was done in the first half.
Believe it or not, Watford have performed well in the second half but they have been overrun by a rampant Manchester City.
Hat-trick! Sergio Aguero is just ridiculous.
The Argentine is picked out by Kyle Walker and he makes a surging run into the box and, despite pressure from various Watford defenders, he manages to curl the ball over the line.
Leroy Sane shoots into the side netting after Watford lose the ball in their own half, but the flag was already up against the City sub.
There's no let-up for Watford here...
The shaven-headed David Silva makes way for Leroy Sane. So much quality in this City squad.
Manchester City have had 70% of the ball and 20 shots at Vicarage Road.
David Silva is in the heart of things, 84 touches in all, completing 94% of his passes, with two assists.
Kevin De Bruyne left the field with 89 touches. It looks like Silva will outshine him today.
Raheem Sterling is flat on his face in the box, looking forlorn, after a tame strike with his right foot trickles wide of the target. He was set up beautifully by Sergio Aguero.
Christian Kabasele came in on Sterling and the Watford defender has hurt himself in the process.
A final switch for Watford, as Troy Deeney replaces Andre Gray.
Watford are shouting for handball, but it's half-hearted. After seeing the replay, John Stones definitely used his head.
The resulting corner comes swinging in and Etienne Capoue *almost* squeezes a header into the top corner. It's just wide of the far post!
Another change for Watford now, with Etienne Capoue coming on for Nathaniel Chalobah.
Capoue has scored in his last two games for the Hornets.
Loads of subs coming now.
For Watford, Roberto Pereyra is on for Tom Cleverley.
City meanwhile, make two changes. Bernardo Silva comes on for Gabriel Jesus, while Kevin De Bruyne gets a rousing reception as he's replaced by the returning Ilkay Gundogan.
After Gomes' wonderful save, Manchester City take a quick corner.
It's whipped in by David Silva, into the path of John Stones, but it's Nicolas Otamendi who heads it home for City's fourth.
Another chance for Manchester City.
A gorgeous backheel from Sergio Aguero falls into the path of David Silva and Gomes has to save.
Benjamin Mendy's long legs are causing mayhem on the left again.
He has loads of space to make a move and the City wideman forces Gomes into action.
Another Watford corner, taken by Jose Holebas.
Richarlison rises high to it, but his header loops over the target and City have the goal kick, despite Richarlison thinking it had come off a City defender.
Richarlison is down in the area, holding his head after clashing heads with Kyle Walker. It looks like they both went for the ball at the same time and the Watford forward has come off worse.
Manchester City break up the left, and Benjamin Mendy strides forward before taking a cross/shot and it hits the side netting.
Jeers go up around Vicarage Road as Andre Gray is flagged offside. The Watford faithful are convinced at least one of City's goals should have been chalked off by the linesman, and they're making their thoughts known about it.
This is much better from Watford. Andre Carrillo makes a weaving run into the box and earns Watford's first corner of the match.
It's sent in by Holebas and as Nathaniel Chalobah tries to get something on it, he goes to ground under pressure from Kyle Walker.
Chalobah looks in pain. It was a heavy clash of bodies with the City defender, and it was pretty clumsy, but not sure it was worthy of a penalty.
They have a word with the ref anyway.
The corner comes to nothing for City, but frankly I'm too distracted to notice because Gabriel Jesus is wearing GLOVES IN SEPTEMBER.
The game's gone.
Fernandinho is brought down by the little terrier that is Tom Cleverley on the edge of the City box.
The Watford man gets a talking to from the referee after shooting evil stares and some choice words. No card, though.
Now City come forward an earn their first corner of the second half.
Watford make a cool, calm and collected start to proceedings.
Jose Holebas makes some headway up the left, getting past Kyle Walker. Benjamin Mendy heads clear in the box but the ball falls to Andre Carrillo, who takes a decent swipe at goal but it drifts just wide of the post.
As it stands Manchester City will be top of the table, with Manchester United, Chelsea and Newcastle rounding out the top four...
Watford get us back under way in the second half!
This is brilliant! Fans of Watford have reenacted photographs of themselves from the 1980s, with ex-winger John Barnes, as part of launch of a new book about the Hornets.
Barnes hasn't aged a day! Take a look here.
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Well, that escalated quickly.
Andre Carrillo chips forward for Watford, in the hope of finding Andre Gray, but City keeper Ederson gets there first.
He's not had a lot to do in the last half an hour. Glad to see he's still awake.
Ex-Chelsea winger on 5 live Sport
I have no idea what Watford can do. In every single area of this pitch, Manchester City look dangerous.
This is very, very scary. Not just for Watford, but for every team!
Tom Cleverley picks up the ball in his own half and punts it long for Richarlison, but it's not precise enough and City are back in possession.
Kevin de Bruyne's free-kick causes no danger for Heurelho Gomes, which he must be thankful for after conceding three in a short space of time.
Abdoulaye Doucoure is booked for tangling with Raheem Sterling and Manchester City earn a free-kick in a dangerous position, about 20 yards out.
But should that have been given? Gabriel Jesus looked off side when he received a cut-back from Sergio Aguero and slides the ball past Gomes.
Jesus has a look at the linesman before celebrating but the flag stays down.