A much-changed Chelsea weathered the storm to navigate their way past a tricky Watford side and stay top of the Premier League with a 2-1 win at Vicarage Road.
With Liverpool and Manchester City also winning on Wednesday, Chelsea found themselves third in the Premier League with 20 minutes remaining, but regained top spot with what Thomas Tuchel described afterwards as a "lucky" victory.
Play was halted for half an hour early in the first half for a medical emergency in the stands, with officials being alerted to the situation by players. Watford later confirmed a fan was stable after suffering a cardiac arrest.
Chelsea took the lead just before the half-hour mark as two of their six changes combined, Mason Mount converting at close range from an unselfish assist by Kai Havertz.
But Claudio Ranieri's Watford caused his old side headaches throughout, deservedly levelling through Emmanuel Dennis' deflected effort off Antonio Rudiger (43).
Chelsea's summer signing Saul Niguez was hooked at half-time again - he was also brought off at the break in his only other Premier League start in September against Aston Villa - but after keeping Watford out for most of the second half, the leaders retook the lead through sub Ziyech's finish from a Mount centre (72).
The defeat leaves Watford 17th, three points above the drop zone.
- Fan 'stable' after cardiac arrest at Watford
- How the teams lined up | Match stats
- Premier League table | Fixtures
- Get Sky Sports | Live football on Sky Sports
How leaders escaped Watford with fortuitous win
Watford dominated the first 10 minutes - Chelsea had just two touches in the opposition half in the early stages - and came close twice; first, Trevoh Chalobah blocked superbly from Joao Pedro's low drive, before Edouard Mendy did well to stop a second Pedro effort, parrying away to his right.
But on 13 minutes, referee David Coote brought both sets of players off the pitch after being alerted to a medical emergency in the Graham Taylor Stand. The game was halted for a total of 30 minutes, and Watford later confirmed a fan had been stabilised having suffered a cardiac arrest.
As play resumed after a five-minute warm-up, Chelsea finally settled and struck the post through Mount at an acute angle, before Watford were left to rue not making more of their early dominance as the visitors carved them open.
Marcos Alonso expertly took down Rudiger's ball over the top, cutting it back for Havertz, and the German laid it on a plate for Mount to fire into the bottom corner from close range, his first Premier League away goal since March.
But Watford recovered quickly and continued to trouble Chelsea, levelling through the bright Dennis for his sixth goal in the Nigerian's debut Premier League season. As Ruben Loftus-Cheek cheaply lost out in midfield to Moussa Sissoko, Dennis was found and struck low towards the bottom corner, the ball helped into the net via a slight deflection off Rudiger. It was no less than Watford deserved.
The first-half action did not end there as Dennis returned the favour and slipped Sissoko in behind the line of defence, but he should have done better as Mendy got down to save well.
Chelsea felt aggrieved just before the break as William Troost-Ekong piled in on Mount, but was only booked by Coote, before Thiago Silva replaced Saul in an attempt to shore things up for Chelsea at half-time.
It barely worked as Watford created a fine chance to take the lead - Pedro played in Tom Cleverley, Mendy boldly raced outside his box, but was able to block without using his hands - prompting Tuchel to attempt to swing things again with an attacking sub, bringing on Romelu Lukaku for Cesar Azpilicueta with 20 minutes left.
But it was fellow sub Ziyech who put them ahead against the run of play, finishing high into the net from 12 yards from Mount's cut back from the left flank. Watford goalkeeper Daniel Bachmann, who got a touch to the shot, could have done better.
Ziyech nearly scored another late on, seeing his fierce header from Havertz's cross stopped by Bachmann, and Chelsea finally found some form of solidity at the back to keep Watford at bay for the remaining minutes.
It was not pretty from Chelsea - and they didn't escape unscathed as Chalobah was brought off with a worrying-looking injury - but if Sunday's draw against Man Utd was a case of two points dropped, this was a case of two fortuitously gained.
What the managers said:
Watford boss Claudio Ranieri: "What can I say? It's unbelievable what happened, but that's football. I am very satisfied and proud of my players. We must continue in this way.
"We played very, very well. Maybe in some matches we don't play well and pick up three points! If we continue this way, I truly believe we will be safe."
Chelsea boss Thomas Tuchel: "It was very sloppy, but it was very unusual from us. I had the feeling we were not ready. I am involved in that, I have to get the team ready and obviously I didn't prepare them for what was coming. We did not cope well with the first balls, the pressure, the second balls.
"It's one thing to win or lose challenges, but we did not even find them. We had the chance to speak about it in the break, and then we had the chance to speak about it in half-time. We tried to give easy messages, because it was obvious we struggled.
"I think we can admit today we were lucky to win this game. It was a very unusual performance for us, and I will not focus on this match for long."
Opta stats
- Watford have lost five of their seven Premier League games under Claudio Ranieri (W2), conceding 16 goals in total - an average of 2.3 per game.
- Chelsea have won five consecutive Premier League away games for the first time since November 2019, under Frank Lampard - a run that also included a 2-1 victory over Watford.
- Despite winning 2-1, Chelsea completed just 71% of their passes (285/399) against Watford, their lowest passing accuracy in all competitions under Thomas Tuchel and their lowest in a Premier League game since May 2018, against Liverpool.
- Chelsea have made 50 changes to their starting XI after just 14 Premier League games in 2021-22 - the fewest matches in a season to make as many since Manchester United did so in their opening 14 games in 2009-10.
What's next?
Watford now host Man City at 5.30pm on Saturday Night Football, live on Sky Sports Premier League, while Chelsea are at West Ham at 12.30pm on Saturday.