The result comes after Tottenham missed the chance to go third as their Wembley woe continued against Swansea City on Saturday evening.
Despite boasting over 75 per cent possession, according to Opta, Spurs were unable to find the breakthrough against Paul Clement’s side as their winless run at their temporary home remains.
Pep Guardiola’s men leapfrogged neighbours United to move three points clear at the top, though Jose Mourinho’s men will return to the summit with a comprehensive victory over Everton on Sunday.
EPL Table | Premier League 2017-18 season table
Two goals from Sergio Aguero put City on course for victory before Gabriel Jesus put the game well beyond the hosts before the break.
Nicolás Otamendi then added a fourth after the interval before Aguero completed his hat-trick late on as Watford’s unbeaten start to the season was ended in emphatic fashion.
Elsewhere, Liverpool slipped up as they looked to respond following last week’s drubbing at Manchester City.
Jurgen Klopp’s men were thrashed 5-0 in Manchester last week and had to come from behind to take a point off Sean Dyche’s Burnley at Anfield.
West Ham continued their recovery with an impressive point at West Brom after victory over Hudderfield on Monday.
Meanwhile, Crystal Palace remain fansitedbusred to the bottom of the Premier League after a fifth loss of the season in Roy Hodgson’s first game in charge.
For the second successive game, the Eagles conceded early on and failed to find an equaliser as their search for their first points and goal of the season continues.
Shane Long netted after six minutes and it proved enough as Hodgson returns to the club he started his playing career at with a loss.
Southampton are ninth as Palace’s dire form continues.
On Friday night, Jermain Defoe fired Bournemouth to their first win of the Premier League season to relieve mounting pressure on boss Eddie Howe.
The 34-year-old rifled his first Bournemouth goal in 16 years, as the Cherries came from behind to sink visitors Brighton 2-1.
Solly March’s header had Brighton dreaming of a second successive Premier League win but Andrew Surman coolly levelled before England poacher Defoe stole the victory.
Defoe last scored for Bournemouth on a loan spell in May 2001, and the veteran exhibited all his stunning staying power to settle this south coast derby.