Chelsea were "lucky" to remain at the top of the Premier League after being given a scare in their victory at Watford, said boss Thomas Tuchel.
The under-par Blues needed a goal from substitute Hakim Ziyech to edge out their hosts after Hornets forward Emmanuel Dennis had cancelled out Mason Mount's opener.
"We were not ready for this game," said Tuchel.
"We are to blame. We never found the right attitude. We were very lucky to escape with the win."
Watford had twice gone close to taking the lead when England midfielder Mount broke the deadlock with a first-time finish at the end of a lovely move involving Marcos Alonso and Kai Havertz.
The Hornets equalised after Ruben Loftus-Cheek lost possession and Moussa Sissoko set up Dennis, who scored with a shot that deflected off Antonio Rudiger.
But having scored his side's first, Mount then set up the winner by providing the pass for Ziyech to fire past Daniel Bachmann.
Chelsea's fifth straight Premier League away win kept them one point clear at the top.
The game was halted for 32 minutes with the score 0-0 while a fan, who had suffered cardiac arrest in the stands, was stabilised.
In a bruising contest which featured seven yellow cards, Chelsea were a long way from their best.
But Tuchel's side found a way to secure a hard-fought three points and maintain their advantage at the summit.
Even before the game was stopped in the 12th minute, Watford had twice gone close. But then Mount - who had earlier hit the post - swept the visitors into the lead.
Dennis' fourth goal in five league games arrived shortly before half-time to lift the hosts, and it could have been even better for them.
Tom Cleverley found himself in a one-on-one with Edouard Mendy but slipped at the crucial moment after the Chelsea keeper came rushing out of his box.
It proved a costly miss as Ziyech, sent on after Trevoh Chalobah was injured, condemned Claudio Ranieri's side to a sixth defeat in eight league games.
However, there were positives in defeat for Ranieri who, after last month's win over Manchester United, saw another spirited home performance from his players.
"We must continue this way and sooner or later the points will arrive," said the Watford boss, whose side remain 17th in the table and host second-placed Manchester City on Saturday.