It was far from plain sailing for the Blues, however, and Thomas Tuchel will likely file this one in the ‘getting three points without playing particularly well’ category. It makes them all the sweeter.

After a 30-minute interruption early in the first half so a supporter in the stands could receive emergency medical treatment (they are thankfully in a stable condition), Mason Mount put us ahead with an assured finish from Kai Havertz’s pass.

Watford had threatened to go in front before then, though, so it was no great shock when, shortly before half-time, Emmanuel Dennis became the first player to score against us on our Premier League travels since Mohamed Salah converted his penalty all the way back in August.

A disjointed second half was lit up by sub Ziyech’s emphatic finish from Mount’s inviting centre with fewer than 20 minutes remaining. Edouard Mendy made a couple of important saves and the Blues’ rearguard action got the job done in the closing stages to keep us top of the table heading into Saturday’s lunchtime date with West Ham.

The selection

Tuchel made six changes to his starting XI across defence, midfield and attack as our busy December got underway on an icy night in Hertfordshire.

Saul started his first Premier League game since his Blues debut on 11 September, and there was a new-look attack with Mount and Christian Pulisic flanking Havertz. Reece James’s 100th Chelsea appearance will have to wait with injury ruling him out tonight, Cesar Azpilicueta the natural replacement at right wing-back.

In the heart of defence, Andreas Christensen was handed a first start since the international break in place of Thiago Silva. Pre-match injury doubts Timo Werner and Jorginho joined the Brazilian skipper and Romelu Lukaku on the bench.

Watford’s in-form striker Dennis was deemed fit enough to play having limped off against Leicester on Sunday.

On pause early

Chelsea started sluggishly. Inside three minutes Trevoh Chalobah needed to be alert to clear Joao Pedro’s shot to safety after Tom Cleverley had outmuscled Marcos Alonso near the touchline and crossed.

Another delivery from the right, this time from Kiko Femenia, was met by the unmarked Pedro, whose header was clawed away by Mendy. The keeper’s next touch, with his feet, was less assured, but he was able to clear before Josh King could tackle him.

Both clubs’ medical teams had already been on the pitch in the opening stages to deal with player knocks when it became apparent a spectator in the Graham Taylor Stand required urgent attention.

Play was stopped and the teams returned to the dressing rooms. Chelsea’s medical staff ran to assist the paramedics in the stands with their Watford counterparts treating the Hornets’ left-back Adam Mesina.

It emerged the supporter had suffered a cardiac arrest but thankfully was stabilised before heading to hospital. Play was paused for half-an-hour in total. Upon their return to the pitch, the teams warmed up for five minutes before the game restarted with 12 minutes on the clock. Mesina was replaced by Danny Rose.

Watford again began on top, but our first attack of note very nearly brought the game’s first goal, as a Ruben Loftus-Cheek header was allowed to reach Mount racing in behind. From a narrowing angle the no.19 opted to shoot, crunching the left-hand post behind which the travelling support were housed.

Goals exchanged

The contest remained bitty, Watford’s direct approach lending itself to fouls from both sides, but Mount would soon be celebrating his fourth goal of the season.

Again it was a fairly innocuous run from deep that carved our hosts open, this time Alonso the beneficiary of a Rudiger pass. The Spaniard’s first touch was immaculate, allowing him to pick out an unmarked Havertz. He quickly moved the ball on to the equally vacant Mount, who made no mistake from six yards out. Half-an-hour gone and the Blues were 1-0 up.

Watford passed up a fine chance to level five minutes later, Danny Rose shooting straight at Mendy as a deep cross was allowed to reach him at the far post.

There would be no such reprieve with the interval a few minutes away. Loftus-Cheek was dispossessed on halfway by Moussa Sissoko and Watford broke at speed with numbers over. Dennis received the ball, drove forwards and went for goal, the shot taking a nick off Rudiger and nestling in the bottom corner.

A lengthy period of added time and three bookings later, referee David Coote finally blew up, bringing to an end a half which had started almost 90 minutes earlier.

Watford merited their leveller and Tuchel reacted to his side’s indifferent performance by changing personnel and shape at half-time. On came Thiago Silva for Saul. Chalobah stepped into midfield, where Mount accompanied him by dropping deeper, the 3-5-2 formation resembling that used on occasion earlier this season.

Battling to break through

Both teams continued to look most dangerous on the counter when possession was turned over, with breaks at both ends wasted in the early stages of the second period.

There was a real scare shortly before the hour when Tom Cleverley was released with all in blue bar Thiago Silva and Mendy ahead of the ball. Our keeper came rushing out of his box to close the former Man United midfielder down and successfully blocked his path to goal, taking a knock in the process. After our medical team had treated Mendy, Chalobah was next in line for attention having been injured in the build-up to the Cleverley chance.

Unlike Mendy he was unable to continue. Hakim Ziyech came on and we reverted to a 3-4-3. Lukaku was our final sub, for Azpilicueta, so Pulisic shifted to right wing-back. Could we find any sort of fluency with 20 minutes remaining?

The answer was yes! Alonso headed Mount free down the left channel and his low cutback was perfect for Ziyech, who slammed a shot high past Daniel Bachmann.

Ziyech then took a blow to the head, necessitating yet another pause for treatment as the fractured nature of the contest continued. The Moroccan almost doubled his tally and killed the game with eight minutes left, getting his head to an inviting Havertz inswinger. Unfortunately, it was too close to Bachmann.

More stoppages followed, and six minutes of added time included a rasping Juraj Kucka free-kick Mendy had to tip over, but the Blues battled across the finishing line to earn a precious three points and get our busy December up and running with a victory.

What's next?

The Blues are back on our travels this weekend, a quick turnaround for the trip east to West Ham at 12.30pm on Saturday.

Chelsea (3-4-3): Mendy; Chalobah (Ziyech 60), Christensen, Rudiger; Azpilicueta (c) (Lukaku 69), Loftus-Cheek, Saul (Thiago Silva h/t), Alonso; Mount, Havertz, PulisicUnused subs Kepa, Sarr, Barkley, Jorginho, Hudson-Odoi, WernerScorers Mount 29, Ziyech 72Booked Saul 16, Alonso 45+2, Ziyech 65

Watford (4-2-3-1): Bachmann; Femenia, Cathcart, Troost-Ekong, Masina (Rose 12); Louza (Kucka 73), Sissoko (c); Dennis, Cleverley (Ngakia 85), Joao Pedro; KingUnused subs Elliot, Hernandez, Gosling, Fletcher, Tufan, KabaseleScorer Dennis 43Booked Louza 45, Troost-Ekong 45+5, Cleverley 84

Referee David CooteCrowd 20,388