Osaka, who is currently ranked No 59 in the world, last featured during the China Open in September where she made it to the round of 16 before retiring injured against Coco Gauff.
The four-time Grand Slam champion took more than a year out of tennis after she became a mother for the first time in July 2023 before returning to action in January, and was handed a wildcard into the US Open.
Mouratoglou, who worked with Serena Williams for a decade, and more recently has been helping guide Osaka, told Sky Sports: “[With] Serena, motivation was extremely key after she beat the record of [Martina] Navratilova and Chris Evert [to reach 23 Grand Slam singles titles].
“But I think we worked so well together because I think we were both motivating each other all the time. I knew exactly how to talk to her. She knew exactly how to talk to me. I was pushing her, she was pushing me and that was like that every day.
“So that’s why it works so well. For Naomi, it’s different because she really feels she has to give and do much more. She had two very difficult years.
“First, she had this mental health issue, and then she had a baby. So she’s been out, and then she restarted the year this season and it was not a very good season.
“Before the first tournament we did together she was 80 in the world and she knows she can do much more than that.
“She’s extremely motivated to come back and win Grand Slams, and it’s a pleasure for me because that’s the dream of every coach: to have a player who has that level of motivation.”
‘I don’t want to have any regrets’
The 26-year-old split with Wim Fisette, who she won two of her four Grand Slam titles with, earlier in September.
Osaka said she was initially hesitant about working with Mouratoglou.
“The fact that he was Serena’s coach made me want to avoid him just because his persona is so big,” Osaka said.
“This isn’t rude because I found out it’s not true, but I didn’t know if he was a good coach or he coached Serena.
“Then I met him, talked to him, worked with him on the court. He absolutely is a really good coach.”
Mouratoglou has been working with Osaka for just over a month and she believes she is at a stage in her life where she does not want to have any regrets.
Mouratoglou sees their relationship as having a good base, with Osaka having approached him first.
“Naomi came to me. I never come to players. I don’t do that. I think it’s weird. I think to work well it’s very important that a player expresses the motivation to work with you,” Mouratoglou said.
“Then there is an extremely good base to start something very solid.
“When a coach goes to a player to say, ‘I would like to work with you’, I don’t think it puts him in a good position to work well.”
‘I don’t feel like I’m in my body’
The 2018 and 2020 US Open champion has failed to go beyond the quarter-finals at any tournament this season.
Osaka revealed she had “suffered long bouts of depression” after withdrawing from the French Open in 2021 and opting not to compete at Wimbledon, although she did contest the Tokyo Olympics in her native Japan.
She likened her loss in qualifying for the Cincinnati Open in August to “being postpartum”, adding in an emotional post on Instagram that the feeling “scares” her.
