Iga Swiatek won the battle of the grand slam champions against Sofia Kenin to reach the second round of the Australian Open.
Kenin lifted her only major title here in 2020 before losing to Swiatek in the French Open final the same year but has struggled since with injuries and a loss of form.
The American remains a dangerous player, though, and knocked Coco Gauff out in the first round of Wimbledon last year.
She served for the opening set before Swiatek fought back to take it in a tie-break, and the Pole was the steadier in the second to claim a 7-6 (7-2) 6-2 victory.
"For sure, it wasn't the easiest first round," said the world number one. "She played really well. I tried to find my rhythm, especially in the first set. I’m happy at the end of the set I could win the most important points.
"I’m happy that I am through and I could play a little bit better in the second set."
Remarkably, Swiatek was the only player in her initial section of the draw not to have made an Australian Open final.
Next she will take on another American in Danielle Collins, who ended Swiatek’s best run in Melbourne so far by beating her in the semi-finals two years ago before losing to Ashleigh Barty.
That is Collins' only victory in five meetings with Swiatek, who won their most recent match 6-1 6-0 in Cincinnati last summer.
"I can’t say that I have an easy draw here," said Swiatek. "I’ll try to do my best. Danielle is a really good player. We played really tight matches. On the other hand, our last match, from the score, I had it under control.
"Every match is different. I’m not going to anticipate anything. I’m just going to be ready and we’ll see."
Collins was a 6-2 3-6 6-1 winner over former Australian Open, Wimbledon and US Open champion Angelique Kerber.
The German is part of a quartet of mothers making their Melbourne returns along with Caroline Wozniacki, Naomi Osaka and Elina Svitolina.
"It is for sure different to be back like this," said the 35-year-old. "I think I’m open more than before, and also the other players are. I’m also more relaxed so I feel that they appreciate it and I think it’s nice to see so many moms are back on tour.
"It is a long way to be back and to play on a high level again. But, on the other side, I have the experience, I know how it is. I played so many grand slams over the years. So I’m more trying to find my rhythm, to being on court and feeling good again."
There were also victories for two other former grand slam winners, with 18th seed Victoria Azarenka beating Camila Giorgi 6-1 4-6 6-3 and Sloane Stephens seeing off Olivia Gadecki 6-3 6-1.
Emma Raducanu made a convincing grand slam return with victory over Shelby Rogers.
Playing her first major tournament since a second-round exit to Coco Gauff here last year following surgery on both wrists and one ankle, the 21-year-old produced an assured performance to beat the American 6-3 6-2.
A packed arena showed how much interest there is in Raducanu's comeback, and this was the sort of routine win she will hope to achieve regularly throughout the season.
Katie Boulter defeated Yuan Yue for her first Australian Open victory in five years.
The British number one has lost in qualifying in Melbourne the previous two years but made rapid strides up the rankings in 2023 and was impressive in a 7-5 7-6 (7-1) win over in-form Yuan.
The only missed step from Boulter, who has been subject of a lot of attention as the girlfriend of Australia's big hope Alex de Minaur, was two match points that went begging on her own serve at 5-4 in the second set.
But she regrouped well and dominated the tie-break for just her second main-draw victory at Melbourne Park.
Third seed Elena Rybakina, who lost to Aryna Sabalenka in the final 12 months ago, saved three set points in the first-set tie-break before beating Karolina Pliskova 7-6 (8-6) 6-4, while fifth seed Jessica Pegula was a 6-2 6-4 winner over Rebecca Marino.
