In a game of constant action and frequent errors it was Chelsea’s false nine who provided the true quality, Eden Hazard scoring twice as the visitors returned to the top four after a few hours’ absence, their advantage over fifth-placed Arsenal extended to two points.

The Belgian scored his 100th goal for Chelsea in first-half stoppage time, set off on the path to his second century with a penalty in the 58th minute, and had his teammates’ finishing matched his own he might have had a hat-trick of assists as well. Hazard has now claimed three goals and set up five more in his last six league games and either scored or created 19 goals in the top flight this season, more than any other player.

It was Hazard who set up Willian for the game’s first clear chance in the 10th minute, the Brazilian running into the area and rounding Ben Foster but shooting against the outside of the post from an acute angle. Watford’s Christian Kabasele collided with the same post as he attempted to protect his goal, the Belgian swiftly substituted and ending the game undergoing tests in hospital.

In the 72nd minute Hazard set up Willian again with a pull-back from the left, the Brazilian this time controlling before spearing a shot narrowly wide of the far post, and seven minutes later his excellent return pass to Kante preceded another effort off target. But though Hazard was integral to his side’s finest moments he was sometimes guilty of floating around its fringes, and was also responsible for the most glaring of the night’s many misses when he allowed César Azpilicueta’s driven cross to pass through his legs as he attempted a clever flick when any kind of contact was likely to prove sufficient.

“He’s a player with special quality, with speed, skilful and it’s difficult to stop him,” said Watford’s Javi Gracia. “Not only him, all of them are very good players and we needed to work constantly and be very disciplined.”

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It took until first-half stoppage time for the game to witness its first shot on target, whereupon two goals were scored in three minutes. First Étienne Capoue gave the ball away in midfield. Mateo Kovacic took control, played in Hazard and the Belgian rounded Foster before passing into the net. A minute later Watford might have equalised after Deeney’s header set up Abdoulaye Doucouré, who had already seen one effort blocked and another go high, for a shot this time saved by Kepa Arrizabalaga. From the corner José Holebas lifted the ball to the edge of the area and Roberto Pereyra rifled a volley into the corner of the net, the second time this season that a similar routine has led to a goal.

The start of the second half was Watford’s finest period of the game, but though they exerted a measure of control all they created was a penalty appeal, after David Luiz, who was repeatedly troubled by the Spaniard’s pace, forced Gerard Deulofeu to the ground in the 54th minute.

Four minutes later Martin Atkinson was pointing to the spot at the other end, after Jorginho lifted an excellent pass over the defence and Foster, obviously deciding that having already been rounded twice he was not going to let it happen again, brought Hazard down. From the penalty spot Hazard sent him the wrong way once again.

This time Watford could not wrestle their way back into the game. Though Deeney shot high from Doucouré’’s low cross with 10 minutes remaining Chelsea seemed more likely to extend their lead than to lose it. Their final chance to do so came in stoppage time when Foster, having come up for a corner, attempted an outlandishly optimistic overhead kick from 20 yards and was then stranded upfield as the visitors worked the ball to N’Golo Kanté, whose reluctance to shoot from distance allowed the goalkeeper to sprint back.

Chelsea’s evening was sullied by apparently minor injuries both to Pedro and to his replacement, Callum Hudson-Odoi, taken off five minutes from the end, and by the reported return of racist chanting from some Chelsea fans. “I don’t want to generalise, because 99% of our fans are really very good, wonderful,” said Sarri. “Then in every community I think there are some stupids, and so all together we have to fight against the stupid people.”