Shortly after last year’s US Open final Naomi Osaka found herself on American television, part of the traditional post-tournament round of commitments for the new champion. At 20, Osaka was the first Japanese player, woman or man, to win a grand slam title, her victory over Serena Williams an illustration of her talent and her ability to stay calm under pressure, remaining cool while her opponent suffered a meltdown.

Osaka was guest of honour on The Ellen Show, hosted by Ellen Degeneres, where she was asked a series of questions about herself, all of which she answered well, even if the experience was not altogether enjoyable. Sitting in a small room in the media centre at the Australian Open, the 21-year-old winces at the memory. “Yikes,” she says. “It was very stressful and nerve-racking because I didn’t see [Ellen] until I walked on, and then from there it felt very odd because I’ve always watched her, she’s either on the TV or the computer.”

In the end Osaka enjoyed herself, even when Ellen teased her, asking her if she had a crush on the actor, Michael B Jordan, before texting him as Osaka sat a little uncomfortably. Since then, and even before then, Osaka has earned a reputation for her personality, especially her humour, intentional or otherwise.

In TV interviews or press conferences, where some players choose to hide behind cliches, talking about round by round or their next match, Osaka is honest and at times, laugh-out-loud funny.

On Saturday, having come from a set and a break down in Melbourne to beat Hsieh Su-wei of Taiwan to reach the last 16, she was asked to explain why, when she had fallen down at one stage during the match, she answered the umpire’s inquiry as to whether she was OK, with a simple: “No”.

“That’s just funny to me,” she says. “He was like: ‘Naomi, are you OK?’ I mean, I was, but I wanted to see his reaction if I said no.”

After one press conference early in her career, she told reporters that everyone born in Osaka, as she was, was called Osaka. It was only when she broke into a smile that they realised she was joking.

Already a hero in Japan – if not yet as famous as Kei Nishikori – she has signed four sponsorship deals since that US Open win, the most recent with All Nippon Airlines on the eve of the Australian Open. Being herself is paying well but Osaka is not sure just how sensible it is.

“For me I feel like it would be better if I wasn’t myself, in a way,” she says. “Because I really admire the other players, who can go in there very serious and talk about things and don’t stray off their story. I feel like I do that a lot. I just feel like it would be better if I was more … serious.

“If when someone asks me a question, if I could just focus on not joking, I think that would be great, because for some reason I can’t. With some of the journalists I’ve known them for years now and I kind of consider them like my friends, so I always tend to joke around and some people don’t get it.”

With almost $8m in prize money, Osaka is not your average 21-year-old, as she readily admits. “I don’t know if I’m ‘normal’,” she says.

She is not. She is a superstar, a woman who could yet go on to win numerous grand slam titles, perhaps even this week in Melbourne, where she could yet face Serena Williams again, should both get to the semi-finals. The difference between now and even last year is that, having been the hunter for the first couple of years of her career, she is now the hunted.

Hsieh almost got the better of her on Saturday, her slice-and-dice style causing Osaka more than a few headaches. The racket went flying a couple of times but she got through it, into the last 16, where she will play Anastasija Sevastova of Latvia.

In New York Osaka cried at the trophy ceremony as sections of the crowd booed, thinking Williams, who was warned and penalised a point and then a game for code violations, had been hard done by. As a young girl growing up in Florida, Williams was her idol. Should they meet again, it is bound to be emotional but she seems resilient, able to channel pressure into a positive.

For some players, winning a grand slam event can release the pressure but for others it can add to the expectation and a worry that people think they should win every time they step on to the court. Osaka, though, seems to relish the big occasions.

“I enjoy grand slams the most,” she said. “I don’t really feel that much different. A lot of people ask me how I feel after the US Open. But for me, it feels like a fresh start. I’m just really excited every time I play a match.

“I don’t feel pressure,” she says. “I feel nerves, if that makes sense. I felt really nervous in the first round but after that I felt really good. I have been playing really well, so for me, grand slams are more of an exciting time.”

Whatever happens over the next week, she is likely to see the funny side.