Raheem Sterling was the hat-trick hero as Manchester City opened up a four-point gap at the top of the Premier League, as Pep Guardiola’s team continue their pursuit of an unprecedented quadruple of trophies.

His goals came in the space of 13 minutes at the start of the second-half as City cut loose, having been frustrated throughout the first period on an evening when Watford were threatening to be very awkward opponents. But there was a huge amount of controversy about the goal which changed the game in the 47th minute when referee Paul Tierney overturned the initial decision of his assistant to flag for offside.

Sterling had the ball in the net when his effort looped over Watford goalkeeper Ben Foster, but he had been in an offside position when Sergio Aguero had touched on Ilkay Gundogan’s lofted pass.

However, the ball had been kicked on to Sterling’s shin by defender Daryl Janmaat, and so the referee was happy to award the goal after a long dialogue with his assistant, much to the dismay of the Watford defenders. With that, the game changed in City’s favour and the points were never in doubt as the pressure now switches to Liverpool, who face Burnley at Anfield on Sunday lunchtime.

There had been eyebrows raised before the game when the Watford team-sheet revealed seven changes to their starting line-up from the previous game.

Captain Troy Deeney and in-form winger Gerard Deulofeu were both on the bench as manager Javi Gracia appeared to have one eye on next Saturday’s FA Cup quarter-final at home to Crystal Palace.

Up against the usual packed visiting defence, City wanted an early breakthrough to make life simpler, and David Silva beat Foster to Riyad Mahrez’s in-swinging cross, but the little Spaniard glanced his effort beyond the far post.

When Foster was beaten, everyone inside the ground expected the net to bulge, but Aguero somehow headed wide from six yards after he had been picked out on the six-yard line by a delicious cross from Bernardo Silva.

Watford had lost their seven previous league meetings with City, but they were putting up a very resolute display in defence, although Foster was called upon right at the end of the half to push behind a snap-shot from a tight angle by Aguero as City tried to find the all-important breakthrough.