Serena Williams reaches semi-finals of the Auckland Classic

The 23-time grand slam winner will now take on Anisimova, while Osaka seals her spot in last four of Brisbane International

Serena Williams defeated Laura Siegemund in straight sets at the Auckland Classic on Friday. Getty

Serena Williams wore down a tenacious Laura Siegemund to make the Auckland Classic semi-finals on Friday, as the 23-time grand slam winner chases her first title in three years.

Germany's Siegemund had upset US teen prodigy Coco Gauff to reach the final eight and kept up the pressure until the first set hit 4-4, when Williams moved up a gear to win 6-4, 6-3 in just under 90 minutes.

Next up for the 38-year-old will be Amanda Anisimova, who defeated Eugenie Bouchard in three sets.

Although still troubled by the Auckland wind, Williams said she was determined to prove herself this week as she uses the competition to fine-tune ahead of the Australian Open.

"The conditions definitely didn't help, so it was good to get through that," she said. “It was good for me to just fight, you know. I’m super fit, but match fitness is a little different, so I think all these matches are really helping.

“She has a really good game, and she stepped up and hit a lot of good winners, so it wasn’t really easy. I just had to step up and play a little better, and hopefully get through it.

“You try to have a more positive attitude, but I got a little negative at the end. It was just so windy."

But she is now in the semi-finals of both the singles and doubles in Auckland and said the court time was beneficial in her bid to win a 24th grand slam in Australia later in the month.

"The body's feeling great. I said I wanted to play singles and doubles here so I knew what I was going to be up against and I'm happy to still be in the tournament," she said.

Anisimova won an error-strewn battle with Bouchard to achieve her "lifelong dream" of playing Williams.

"I said before the tournament in an interview that my biggest wish is to play her before she retires so this is the happiest I've ever been," the 18-year-old said after sealing a 6-2, 3-6, 6-4 over the Canadian.

Caroline Wozniacki reached the semi-finals with a 6-1, 6-4 victory over the 2019 champion, German fourth seed Julia Gorges.

The Dane, who will retire after the Australian Open in Melbourne, will now take on unseeded American Jessica Pegula.

American Pegula, who is yet to face a seeded opponent in the tournament, was up 6-0, 3-2 against Alize Cornet when the Frenchwoman retired hurt with a thigh injury.

Naomi Osaka survived another testing three-setter to beat Dutchwoman Kiki Bertens 6-3, 3-6, 6-3 to advance to the semi-finals of the Brisbane International.

As a result, the 22-year-old will leapfrog Simona Halep to rise to third in the singles rankings as the Japanese prepares to defend her Australian Open crown later this month.

"I tried to defend in my US Open title and that didn't work out so well, so I hope it's better for me this time around," Osaka said after her 14th consecutive win since her last-16 exit at Flushing Meadows.

Two-time grand slam champion Garbine Muguruza crashed out of the Shenzhen Open semi-finals with a straight-sets loss to Ekaterina Alexandrova.

Alexandrova, the Russian fifth seed, won 6-4, 6-3 to set up a final with seventh seed Elena Rybakina of Kazakhstan or unseeded Czech Kristyna Pliskova.