MELBOURNE — Elina Svitolina had to come from behind today against Katerina Siniakova to set up an all-Ukrainian third-round clash with teenage sensation Marta Kostyuk.

The world number four was largely in control but somehow dropped the first set on the way to a 4-6, 6-2, 6-1 win against her 59th-ranked Czech opponent in two hours and 14 minutes.

"I think she played well in the first set but I gave her one break, so I think it was kind of my mistake," said the fourth seed.

But Svitolina cranked up the heat as temperatures rose on Rod Laver Arena, relentlessly overpowering her opponent from the back of the court to take the final two sets in dominant fashion.

"I thought I was going to melt today, was struggling a bit" Svitolina admitted. "Today I had enough sun, I just want to have an ice bath and recover."

Svitolina came into the first Grand Slam of the year in top form after winning the Brisbane International warm-up event after picking up five WTA Tour titles last year, more than any other woman.

And she is eyeing a first career Grand Slam title after her half of the draw -- already shorn of US Open semi-finalists Venus Williams, CoCo Vandeweghe and Sloane Stephens -- saw Russian 15th seed Anastasia Pavlyuchenkova bundled out 6-2, 6-3 on Wednesday.

"Of course, after winning in Brisbane and having a great year in 2017," she said when asked if she could win in Melbourne. "But it’s a Grand Slam and every opponent is determined to win."

She now faces 15-year-old Kostyuk whose fairytale continued Wednesday as she became the youngest player to reach the third round since Martina Hingis in 1996 in beating local wildcard Olivia Rogowska in straight sets.

Venus Williams’ Australian Open conqueror Belinda Bencic ran out of steam Wednesday, failing to keep the momentum going against qualifier Luksika Kumkhum.

The Roger Federer-inspired Swiss stunned Williams in round one, but was no match for the Thai star who moved into a Grand Slam third round for the first time.

Bencic, 20, was never in contention on a searing day on Hisense Arena, slumping 6-1 in the first set before putting up more fight in the second only to succumb 6-3.

Bencic, who made her WTA Tour debut as a 14-year-old, has often been touted as a future potential champion, but she again failed to live up to the hype.

Only Tuesday, fellow Swiss Federer, who won the Hopman Cup this month alongside Bencic, had heaped praise on her.

"She’s still so young, she has a great career ahead of herself. I try to help her where I can," he said.

But he also added: "Still so much to improve."

For Kumkhum, it was a major achievement in her seventh Grand Slam main draw appearance.

She lists her best tennis memory as reaching the second round at Melbourne Park in 2013, which she must now surely revise.

"This is the best win of my career," she said afterwards.

"I kept telling my coach and family that I want to pass the second round, so I’m really happy." — AFP