Raheem Sterling scored a second-half hat-trick, including a controversial opener, as Manchester City beat Watford 3-1 to move four points clear in the title race.

Sterling’s first goal was initially ruled out for offside but after a long discussion, referee Paul Tierney overturned his own decision, with Daryl Janmaat’s attempted block just before Sterling struck ruled as having played the winger onside.

There was nothing controversial about his second goal which arrived less than four minutes later, when Riyad Mahrez played the ball across the six-yard box and left it on a plate for him to slot home.

He made it three for the second Premier League hat-trick of his career just before the hour mark showing superb composure to take David Silva’s pass in his stride before riding two challenges and dinking the ball over Ben Foster.

A much-altered Watford team, who had made seven changes for the game, pulled one back when substitute Gerard Deulofeu slotted the ball under Ederson from Troy Deeney’s flick-on, but that was as good as it got for the Hornets.

Before Sterling had broken the deadlock, Watford had looked relatively comfortable despite resting the majority of their first team ahead of next weekend’s FA Cup quarter-final with Crystal Palace.

David Silva came the closest to opening the scoring, firing just wide from a Riyad Mahrez cross, although replays then spared Tierney’s blushes after showing he had handled the ball in the process of heading it beyond the far post.

Watford failed to register a shot on target in the first 45 minutes, but stood strong against wave after wave of City pressure, with the hosts far from their fluid best and lacking the slick movement and passing with which they have become synonymous.

That resistance finally broke 40 seconds into the second half, but the Hornets had a strong case for arguing that their defence was breached illegally. Sergio Aguero brought the ball down and played it into Sterling’s path, but he was in a clearly offside position.

The assistant referee’s flag was raised and Tierney decided against giving the goal, but spent several minutes with his official discussing the details before it was decided a sliding tackle from Janmaat, which got a nick on the ball just as Sterling was about to shoot and took it onto his standing leg, had played him onside.

Javi Gracia was left incensed on the bench while his players appeared still shell-shocked by the time City doubled their lead four minutes later. David Silva picked out Mahrez on the right of the area, he skipped to the byline and pulled the ball across into the middle and leaving Sterling a simple finish.

Watford still stuck to their gameplan and defended deep, but a third followed just before the hour mark which was all down to Sterling’s work. David Silva slipped the ball inside Janmaat, and after racing onto it Sterling could easily have rushed his finish – but stepped through two challenges and beat Foster and take home the match ball.

Gracia finally attempted a throw of the dice in the form of Deeney and Deulofeu, who combined within 30 seconds of coming on to blot City’s copybook. Deeney’s flick found his in-form striking partner and the Spaniard scored his fourth goal in as many games for a glimmer of hope.

But City breezed their way to victory, nearly adding a fourth when Gabriel Jesus left Ben Foster on his backside but was denied by a fine sliding challenge from Christian Kabasele, ensuring City will end the weekend top of the Premier League.