The Brazil global curled home his first goal since Ocotber to seal a 2-1 win over Newcastle and send Chelsea six points clear of Arsenal in the race for fourth place ahead of next weekend's London derby at the Emirates.
Willian admits he's yet to hear from Chelsea about a new contract.
"At the moment in the defensive phase we are doing very well and one of the reasons, in my opinion, is that Eden is playing in that position", Sarri said.
"As you have seen, today Jorginho was in trouble and on the bench there wasn't a player for that position, so I need a player, I need an option for Jorginho", the Italian explained.
The Blues have scored just 13 goals in their last 11 Premier League games and Sarri is increasingly favouring an attacking focal point of Hazard, rather than recognised strikers Olivier Giroud and Alvaro Morata.
"We've played the top sides and the pressure is nearly more than them that it is on us because they're expected to beat us, and if we can get anything out of those games then it's great". In the last six matches we have conceded only three goals and one was a penalty. We were better in the second half but we need to improve the mental reaction.More news: FBI probed whether Trump secretly worked for Russia
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'But I think the character was good and the most important is to win the game.
Sarri also revealed he has told Chelsea's hierarchy he needs a new midfielder to replace Cesc Fabregas, who joined Monaco on Friday. It depends on the club decision. I don't know the detail.
"We need to try and try and try in training".
And after the game Willian, who has 18 months left on his current deal, said: "My future is here. But I think he is able to do it". "We need to learn to attack spaces, or attack the box with the other players", he said.
The leveller then arrived five minutes before half time, as Clark made amends for being caught out for Chelsea's opener by getting in front of Luiz and powering home a corner.