Chelsea maintained their lead at the top of the Premier League as Hakim Ziyech came off the bench to secure a hard-fought 2-1 victory at Watford on Wednesday.
Thomas Tuchel's side were not at their best at Vicarage Road but had enough attacking quality to emerge with three important points and stay ahead of Manchester City and Liverpool.
After a 32-minute suspension while a fan was treated for a medical emergency, Chelsea took the lead when Mason Mount coolly converted after a well-worked move in the 29th minute.
But Watford deservedly levelled before the break through Nigerian Emmanuel Dennis.
Ziyech came on for injured defender Trevoh Chalobah on the hour and struck the winner 12 minutes later with the outstanding Mount turning provider.
Chelsea lead the standings with 33 points from 14 games, with City on 32 and Liverpool on 31.
Claudio Ranieri's side will take heart from the way they pushed the league leaders but are just one place and three points above the relegation zone.
Tuchel made six changes from the side that drew with Manchester United at the weekend and Chelsea looked disjointed for much of the evening.
Watford were the better team either side of the suspension but fell behind to Chelsea's first move of quality.
The ball was played to Marcos Alonso down the left and he slipped the ball into Kai Havertz who shifted it across to the unmarked Mount who had time to pick his spot.
Watford responded well and equalised when Moussa Sissoko powered forward and played in Dennis whose shot took a deflection on its way past Edouard Mendy.
The hosts could have been ahead with Mendy making a fine save and Sissoko scuffing a decent opportunity.
The quality on Chelsea's bench eventually told, however, as Ziyech came on to secure the points.
Mount was played into space down the left and his low cross was met by Ziyech whose powerful first-time shot beat Watford keeper Daniel Bachmann for pace.