MELBOURNE, Australia (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 No. 1 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 Polish 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 semi-finals 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 No. 1 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," the 24-year-old Russian-born Kazakh said.

"We improve this way, so hopefully we continue."

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.