WATFORD, ENGLAND (REUTERS) - 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 (Dec 1).

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.

"We were lucky. We should admit it. Today we could not reach this level. We were not ready for this game. We are to blame. We never found the right attitude," Tuchel said.

"It got better in the second half. We conceded a lot of chances in the first half and didn't create much. The two situations we had, we scored. We were lucky to escape with the win."

Tuchel accepted some of the blame for his team's approach.

"It felt like we were not ready for the long balls, the pressure. When we won the ball, how to escape out of the pressure. We had big problems individually and as a team. We never felt solid, it felt like we were never in control."

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.

When the dust settles, however, Tuchel might look back on Wednesday as a vital victory in his attempt to keep ahead of City and Liverpool in the title race.

"We need a lot of points if we want to stay in the title race," the German said.

"We felt like we lost two points against Burnley and Manchester United.

"We stole minimum two, maybe three back today. Watford deserved more today."

With another big game at West Ham United on Saturday, Tuchel has an injury worry over Reece James who missed the trip to Watford. "I cannot say today. Yesterday he was in too much pain to travel. He got a kick on the ankle," he said.