MELBOURNE (AFP) -- Iga Swiatek is in scintillating form as she seeks a maiden Australian Open crown, but she could face a stiff test from defending champion Aryna Sabalenka while two-time winner Naomi Osaka is making her comeback.

World number one Swiatek has won 17 of her 18 matches since she lost in the fourth round of her US Open title defense, going on to win the China Open and the WTA Finals.

The Pole has started the new season with a flourish, winning all five of her singles at the United Cup last week.

But the four-time Grand Slam champion knows Sabalenka, who last year became the first woman since Serena Williams in 2016 to reach at least the semifinals of all four Grand Slams, is a huge threat.

The Belarusian overtook Swiatek for the top ranking in September and appeared on course to finish the year as number one until the Pole won the season-ending WTA Finals in Mexico to return to the summit.

The best previous result at Melbourne Park for Swiatek, 22, was reaching the semifinals in 2022.

The 25-year-old Sabalenka was on a 15-match winning streak in Australia before Sunday's 6-0, 6-3 Brisbane International final defeat to Elena Rybakina in a rerun of last year's Australian Open championship match.

The 2022 Wimbledon champion Rybakina, ranked third in the world, will also be one of the favorites for the year's first Grand Slam, which will start on Sunday in a bid to reduce the amount of late-night finishes in the early rounds.

"We always push each other and I think that's great," said the Russian-born Kazakh, 24. "We improve this way, so hopefully we continue."

New moms return

Japan's Osaka and Germany's Angelique Kerber are among a number of mothers returning at the event after giving birth, a group that includes the 2018 winner, Caroline Wozniacki of Denmark

Another recent mum, Ukrainian Elina Svitolina, is seeking to build on her impressive form after coming back in April last year.

She was in great touch in her Auckland warm-up last week, beating former Grand Slam champions Wozniacki and Emma Raducanu before losing a tight three-set final to American Coco Gauff.

Nineteen-year-old Gauff, who won her first major at the US Open in September, rounds out a powerful group of four at the top of the rankings.

Two-time Australian Open champion Osaka returned to the court last week after taking a 15-month break from the game, initially for mental health concerns. Last year she gave birth to daughter Shai.

The 26-year-old stayed upbeat after her second-round loss to Karolina Pliskova in Brisbane last week.

"I think for me even stepping on the court is a personal win because a couple of weeks ago I was even doubting if I could play with everyone," said Osaka.

"I know that if I keep training and if I keep putting in the work, then I'll eventually get to where I want to be."

'Wonderful memories'

Wozniacki, 33, who reached the fourth round at last year's US Open, is playing at Melbourne Park for the first time since 2020, having had two children while away.

"I have so many wonderful memories of Melbourne and, of course, winning the Australian Open is an all-time career highlight," Wozniacki, who was given a wildcard to compete, told the AO Show Podcast.

Britain's Raducanu is also on the comeback trail after an injury-blighted 2023.

The 2021 US Open champion, who boasts a huge media profile and lucrative endorsement deals, has only played twice in Melbourne and has never been past the second round.