The Blues forward has toyed with several opponents during the early stages of the 2018-19 campaign, with no World Cup hangover suffered by one of the finest players on the planet.
Hazard, who has been eased back into domestic action by Maurizio Sarri, is leading a Chelsea charge that has delivered six successive victories across all competitions.
He has contributed five goals to that cause, including a hat-trick in his last outing against Cardiff, with his efforts seeing him showered with praise from inside and outside Stamford Bridge.
Kovacic, who joined Chelsea on loan from Real Madrid over the summer, told BBC Sport’s Football Focus: “For me he has everything, but the thing that has impressed me the most is that they tackle him so much and he is always on his feet.
“England is a really tough league, the toughest in the world for me, and he just plays with the defenders. He’s an incredible player but also a nice team-mate, a nice guy, and I have really enjoyed the time playing with him.
“When I came here I didn’t realise he was so good. He is one of the best players I have played with. The stuff he is doing is amazing; he is helping the team a lot and I hope he will continue like that, or do even better because I think he can do better for sure.”
Hazard’s heroics have Chelsea daring to dream of another Premier League title challenge, having slipped out of the top four last season under Antonio Conte.
Kovacic believes there is more to come from an in-form side, with their next outing set to see them take in a London derby date with West Ham.
“‘It’s important to keep winning. We need to have this mentality to try to win every game, and for now I think we are doing very well,” added a loan star that has impressed in England.
“Everybody can see Chelsea are trying to play attacking football, football that the fans like to watch, so I think we will have a good season this year.
“We can improve a lot because we have great potential, but the team is doing great and that is the most important thing for now.”
Kovacic will be hoping that his initial season-long agreement with Chelsea will deliver tangible reward, but he could be back for more in 2019-20.
A permanent deal may be struck with Real next summer, with the 24-year-old Croatia international ruling nothing out at this stage.
He said when quizzed on his future: “It is too early and I have to respect my contract with Real Madrid.
“But for now I'm really happy with Chelsea. The city is amazing. The fans are great. The stadium, everything is nice. I could imagine myself [staying] here.”