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.
With title rivals Manchester City and Liverpool both victorious, Chelsea would have slipped to third had they drawn - but Ziyech ensured they still lead the way.
"We were not ready for this game," said Tuchel.
"We are to blame.