Mason Mount put Chelsea ahead before Emmanuel Dennis levelled the score, only for Ziyech to come off the bench to seal the points.
James Robson was at Vicarage Road to rate Chelsea’s players.
Edouard Mendy – 7
Crucial block denied Tom Cleverley when the Watford midfielder ran clear on goal. Not helped by Antonio Rudiger’s deflection for Dennis’ goal.
Trevoh Chalobah – 6
Worrying sign when he went down clutching his hamstring. Moved into midfield to try to give Chelsea more control in the second-half.
Andreas Christensen – 6
Tuchel publicly called him out over his contract pre-match, but he was back in the starting line-up with a point to prove. This was a tough night for all of Chelsea’s defenders – him included.
Antonio Rudiger – 6
Moment of ingenuity opened up Watford’s defence for Chelsea’s opener, but could not get a block on Dennis’ shot, which he diverted past Mendy.
Cesar Azpilicueta – 6
Tried to wake his teammates up after such a sluggish start. Struggled to repel Watford’s flying forwards.
Ruben Loftus-Cheek – 7
Not helped by his midfield partner in the first-half. Improved after the break with his driving runs and the quality of his passing.
Saul Niguez – 4
That’s another game to forget for the Spain international. Totally off the pace and substituted at half-time after being given the runaround.
Mason Mount – 8
Fired Chelsea ahead and hit the post with another effort. Good movement up front and then provided the cross for Ziyech’s goal.
Kai Havertz – 6
Very unselfish when setting up Mount for Chelsea’s opener. Picked up good positions in attack to hurt Watford.
Christian Pulisic – 5
Touch let him down on two occasions early in the second half when he could and should have at least worked the goalkeeper.
Thiago Silva (Saul, 46’) – 7
Restored a sense of assuredness to a defence that had looked ragged in the first half. Needed Mendy to save him when Cleverley burst clear.
Hakim Ziyech (Chalobah, 60’) – 7
Came off the bench to turn the match. Ghosted into the box and blasted the ball into the roof of net to fire Chelsea ahead.
Romelu Lukaku (Azpilicueta, 69’) – 5
Tuchel was bold enough to throw him on in a bid to secure the win. His physicality gave Watford’s defenders a fresh problem.
Substitutes unused: Kepa, Sarr, Barkley, Jorginho, Hudson-Odoi, Werner