Serena Williams pulled out of the Yarra Valley Classic with a shoulder problem after reaching the semi-finals of the Australian Open warm-up event.

The 23-time grand slam champion did not mention that anything was amiss after defeating Danielle Collins 6-2 4-6 10-6 in the quarter-finals at Melbourne Park on Friday.

Williams said: “It was a good match. I think Danielle is such an aggressive player. I’m glad I was able to get through that one in a tie-break.”

The 39-year-old had been due to play world number one Ashleigh Barty on Saturday but the Australian will now have a free passage through to the final.

Williams’ withdrawal is likely to be a precaution. In normal times, top players generally do not enter tournaments the week before grand slams and the world number 11 would likely not have wanted to play three consecutive days before the start of the Australian Open on Monday.

Writing on Instagram, Williams said: “I’m really disappointed I can’t finish out this #yarravallleywta tournament going to take a day off to get my shoulder ready for the @australianopen.”

Barty, playing in her first tournament for nearly 12 months, had her own battle against American Shelby Rogers but came through 7-5 2-6 10-6.

The other semi-final will pit sixth seed Garbine Muguruza against former French Open finalist Marketa Vondrousova.

Muguruza won a confidence-boosting rematch of last year’s Australian Open final 6-2 6-2 against Sofia Kenin while Czech Vondrousova, who has struggled since losing to Barty in the Paris final in 2019, defeated Nadia Podoroska 4-6 6-3 10-4.

At the Gippsland Trophy, Naomi Osaka continued her unbeaten sequence but Simona Halep struggled with what appeared to be a back or hip issue in a heavy 6-2 6-1 loss to Ekaterina Alexandrova.

Osaka has not lost a match since last February – a run that admittedly comprises only three tournaments – and is through to the semi-finals after a 7-5 6-1 victory over Irina-Camelia Begu.

In the last four Osaka will face seventh seed Elise Mertens, who upset third seed Elina Svitolina 6-3 5-7 10-6, while Alexandrova will take on Kaia Kanepi.

At the Grampians Trophy, which was hastily arranged for players who endured two weeks of hard quarantine, Victoria Azarenka saved two match points on her way to a 6-4 1-6 (9) victory over Yulia Putintseva.

There were defeats for second seed Belinda Bencic, against Sorana Cirstea, and fourth seed Elena Rybakina, who lost 4-6 6-2 10-6 to Barbora Krejcikova.

Maria Sakkari, Angelique Kerber, Anett Kontaveit and Jennifer Brady all made it through to the quarter-finals.