MELBOURNE, Australia (AP) — It was a meaningless hit-and-giggle session, a mixed doubles exhibition at Rod Laver Arena just for fun and charity in front of fans a few days ahead of the Australian Open, so Coco Gauff was calling out how fast she would try to hit some serves.

Her guesses, and her deliveries, kept getting closer to 200 kph (125 mph) on Thursday evening, Jan. 9, and when the 2023 U.S. Open champion and her partner, Andrey Rublev, had taken that game, one of their opponents, Hall of Famer Lleyton Hewitt, acknowledged, “Great serving.” Gauff's response? “Thanks. I've been working on it.”

Yes, she has — on her serving and her forehand — and the strides made in both of those areas are among the reasons Gauff is considered one of the few women ready to challenge two-time defending champion Aryna Sabalenka for the title at Melbourne Park when the year's first Grand Slam tournament begins Sunday (Saturday EST).

“It would be great to come home with the Australian Open trophy. But I think I’ve just learned to not put so much pressure on events, and just put pressure on development and how I’m playing. That takes the pressure off,” Gauff said. “I mean, yeah, making the semis last year and losing to Aryna, the eventual champion — I feel like I can get there and cross that line.”

Her first opponent in Melbourne will be another American who owns a Grand Slam title: Sofia Kenin, the champion in Australia in 2020 and a winner against Gauff in the first round at Wimbledon in 2023. This match will be Gauff's first appearance at a major since she accumulated 19 double-faults in a fourth-round loss at last year's U.S. Open to Emma Navarro.

With the help of new coach Matt Daly, who joined Jean-Christophe “JC” Faurel on Gauff's team after Brad Gilbert was let go in September, the 20-year-old American adjusted the grips she uses for her forehand and serve in a bid to correct the two most obvious shortcomings in her game.

“It’s just been a great combo. JC has brought me a lot of footwork and shot selection in my game. And Matt has helped me with the technical side of things — my serve, specifically, and other things, as well,” Gauff explained. “It’s just a good combination that we have. I'm very thankful for them to make the transition as easy as possible, especially considering it is two people.”

So far, so good.

“She's, for sure, improving,” five-time Slam champion Iga Swiatek said.

Swiatek had an up-close look, losing to Gauff in the WTA Finals in Saudi Arabia in November and in the final of the United Cup team event last week in Sydney. Both were straight-set results and came after Swiatek had led their head-to-head series 11-1.

As Gauff posted on social media: “new szn, better me.”

The championship at the WTA Finals felt like a big moment. It also included a victory over Sabalenka, who is currently ranked No. 1 — one spot in front of Swiatek, and two in front of Gauff.

“It means a lot to me,” Gauff said, “and playing the best of the best makes me feel confident in my game. ... I want to win as many big trophies as possible and just fill the cabinet up."