Hazard last season expressed frustration about being deployed in such a position under former boss Antonio Conte.
However, Sarri insisted the Belgian liked it after being asked to play there in December's win over Manchester City and frequently since.
The Italian admitted Hazard was unhappy in the first half, but grew into the game against Newcastle.
Hazard's happiness is key to Chelsea, given his contract expires in June 2020 and he has spoken of a daily quandary over whether to seek a 'dream' move to Real Madrid.
"In the second half my feeling was that he enjoyed (it)," Sarri said. "I played him there because I wanted to see the solution with the three small players.
"I think that at this moment it is a very good solution because we are not less dangerous in the offensive phase. And in the defensive phase we are more balanced. In the last six matches we have conceded only three goals and one was a penalty.
"Now we need to improve attacking in the box when the ball is out of the box. It is impossible for Eden to stay in the box."