Chelsea boss Maurizio Sarri admits his players have surprised him with how quickly they've adjusted to his plans.

Sarri expects another tough test on Sunday against West Ham.

"I am surprised because in Naples the beginning was very difficult, the first month," Sarri said.

"Here at the moment I am very happy with the situation, with the players, with the club. But I know the Premier League is a very competitive competition so I know in the future I will have to face some difficulties.

"I have seen the five matches of West Ham in the Premier League, and I think they have been unlucky," continued the boss.

"They changed in the last match against Everton from 4-2-3-1 to 4-1-4-1 and they played very well. Their position in the table is not a realistic one."