Top seeds Carlos Alcaraz and Aryna Sabalenka safely through at Australian Open

Playing at the tournament for the first time since 2021, 45-year-old Williams led Serbian Olga Danilovic 4-0 in the deciding set only to slip to a 6-7 (5) 6-3 6-4 defeat.

Williams, the oldest woman in the open era to contest a singles match at the tournament, said afterwards: “It was such a great game, such a great moment. The energy from the crowd was amazing. That lifted me up so much.

“She played a great game. Also some luck there, as well. That’s just the sport. That’s how it works sometimes. But it was an amazing moment.

“I’m really proud of my effort today because I’m playing better with each match, getting to the places that I want to get to.”

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Alcaraz did not have things all his own way in his first match since last month’s shock split from coach Juan Carlos Ferrero but the 22-year-old, who is bidding to complete the set of slam titles, saw off Australia’s Adam Walton 6-3 7-6 (2) 6-2.

Aryna Sabalenka is trying to win her third title here in the last four years, and she overcame some early wobbles in a 6-4 6-1 victory over young French wild card Tiantsoa Rakotomanga Rajaonah.

The world number one admitted afterwards she was starstruck by a couple of faces in the front row of the stands, ensuring she got a selfie with Roger Federer and Rod Laver.

“I’m a huge fan,” she said. “The whole match I was just telling myself, ‘Do not look there, please, do not look’. It’s incredible. I would never have thought that Roger Federer and Rod Laver are going to be sitting first row watching my match.”

Turkish qualifier Zeynep Sonmez caused the biggest upset of the tournament so far by taking out 11th seed Ekaterina Alexandrova – and earned praise for a notable act of sportsmanship.

While Alexandrova was serving for the second set, Sonmez spotted a ball girl feeling faint courtside and rushed to her aid, helping the youngster into the shade, where she received medical assistance.

Temperatures were not extreme on Sunday, peaking in the high 20s, but there is the possibility of a heatwave next weekend. The tournament’s heat stress scale measures the severity of conditions, with play suspended if it reaches a certain threshold.

Sonmez went on to lose the set but battled through the decider to claim a 7-5 4-6 6-4 victory for the biggest win of her career.

Men’s third seed Alexander Zverev, who reached his third grand slam final here last year, was briefly in trouble against dangerous Canadian Gabriel Diallo but hit back strongly to win 6-7 (1) 6-1 6-4 6-2.