However, Sarri believes Hazard can be even more prolific if he preserves his energy more to make the difference in the final third.
We are still very much in the dark, but Sarri has suggested that we will know the answer soon.
"I told him... for me you can score 40 goals but you have to spend less energy".
His current form comes off the back of a brilliant World Cup where he captained Belgium and won the silver ball, finishing just behind Luka Modric whose displays for Croatia saw him earn the most prestigious individual prize in Russian Federation.
"My target is to be the best team in England, but not in one month", said Sarri, who took over from Antonio Conte in the summer.
According to the Chelsea boss, Hazard is the best player in Europe but needs to be smarter in the way he goes about his business while building-up play.
He said: "No (not defending), when we have the ball in our half and he touches the ball five or six times, it shows he spends a lot of energies, and can have more enegy in the last 25 metres. So yeah, for us it's a pleasure for us to play with him".
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And Alonso started the move for Chelsea's second as he played in Pedro and his cross was expertly steered by Giroud in Hazard's path to score via a deflection.
Cardiff has two points from five games.
City remain just two points back and looked back to their best in tearing apart Fulham 3-0 thanks to goals from Leroy Sane, David Silva and Raheem Sterling. To close that gap in only one season is very hard.
"I think in this moment, we are very unsafe in the offensive phase but we are not so solid as I want in the defensive phase", Sarri said. "We can play, we should play better, but we scored four goals and it's a good game for us".
"We need to improve, and we can improve".
Hazard had the help of a deflection to put Chelsea in front from close range and gave the home side breathing space from the spot after Willian was felled by Bamba.
Hazard fired his first into the bottom corner after dancing round two defenders, then latched on to another Olivier Giroud lay-off for the second.