However, Sarri believes Hazard can be even more prolific if he preserves his energy more to make the difference in the final third.
"I thought that Hazard was one of the best players in Europe. But now I change my mind because maybe he is the best," said Sarri of the man crowned the second-best player at the World Cup this summer.
Hazard struck twice in seven minutes just before half-time to cancel out Sol Bamba's early shock for the hosts at Stamford Bridge before completing his hat-trick from the penalty spot to take his tally for the season to five goals in just three starts.
But Sarri wants his star man to spend more time closer to the opposition goal rather than dropping deep to get attacks started.
"Hazard can improve more. I think he can spend less energy than now at 50 or 60 metres from the opposition goal," added the former Napoli boss.
"I told him... for me you can score 40 goals but you have to spend less energy. You have to play in the last 25 metres."
And Hazard hailed the freedom Sarri's set-up has offered him to get forward and try to improve on his best ever tally of 19 goals for a season in English football.
"(He) just wants us to play and to find space between the lines so then Jorginho, Mateo Kovacic, Cesc Fabregas can find us," said Hazard.
"We have a lot of freedom on the pitch, and at the moment when we try and do something, it's coming off."
Unlikely title challenge
Chelsea rebuffed interest from European champions Real Madrid for Hazard after the player himself declared an interest in moving on after the World Cup.
And that resilience could yet yield an unlikely title challenge after finishing 30 points adrift of Manchester City last season.
Willian's sumptuous strike for Chelsea's fourth edged the Blues ahead of Liverpool at the top of the table on goal difference with City just two points further back.
But Sarri insists last season's champions and Champions League finalists remain the benchmark for his side.
"My target is to be the best team in England, but not in one month. Maybe one season, maybe a little more but our target is this.
"At the moment, for me, in my opinion, Liverpool and Manchester City are better than us."
The feeling of being outclassed is one Cardiff may become accustomed to, having failed to significantly strengthen over the summer on their return to the top flight.
Neil Warnock's men have picked up just two points in 0-0 draws with a man advantage against Newcastle and Huddersfield from their opening five games.
"We have got to learn quickly because these top teams punish you," said Warnock.
Cardiff couldn't have asked for a better start when a well-worked Joe Ralls free-kick was headed across goal by Sean Morrison and bundled in at the back post by Bamba.
However, they had no answer to Hazard's trickery as he dummied a ball into the path of Olivier Giroud and then fired the Frenchman's return pass low into the far corner.
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.
Moments later Willian capped the rout with his own moment of magic with a wonderful curling effort from 20 yards that bent into the top corner.