Defending champion Karolina Pliskova survived a massive scare from Estonia's Kaia Kanepi to move into the semi-finals of the Brisbane International on Thursday.

Second seed Pliskova lost the first set to an inspired Kanepi and was down 3-1 in the second before launching an epic comeback, winning 3-6, 7-5, 6-2 in two hours and 11 minutes.

Pliskova was in imperious form in her demolition of American Catherine Bellis in the last round, but the powerful Kanepi proved a far tougher challenge.

The 32-year-old Estonian won in Brisbane in 2012 but 12 months away from the game with injury in 2016-17 saw her ranking plummet and she had to qualify to make the main draw this year.

Kanepi looked like joining fellow qualifier Aliaksandra Sasnovich in the semi-finals as she outplayed Pliskova at her own power game.

But she faltered when serving to go to 4-1 in the second set, allowing Pliskova to break back and swing the momentum towards the Czech world number four.

"I was a little bit surprised the first set and a half how she played," Pliskova said.

"And for the big risks that she was taking, she had almost zero mistakes," she added.

"The only thing that I could do is just wait for my chance, and I got it, because, obviously, nobody can play like this for two sets or three."

Pliskova will now play third seed Elena Svitolina for a place in the final after the Ukrainian won an eventful match against British number one Johanna Konta.

Svitolina reached the final four when Konta was forced to retire with an injury at 2-3 in the third set.

Konta had raced through the first set before Svitolina recovered to take the second in a tiebreak.

But Konta felt a problem with her right hip in her first service game of the third set and opted to withdraw, with Svitolina winning 1-6, 7-6 (8/6), 3-2.

Svitolina, tipped as a possible winner of the Australian Open, was pleased at her recovery after a sluggish start.

"Playing against a top 10 player early in the year... it can be challenging, but it's good," the Ukrainian said.

"After losing the first set, I was trying to stay calm and to realise what I was doing wrong, and I actually came back in the second set.

The second semi-final will be between Sasnovich and seventh seed Anastasija Sevastova of Latvia.

Sasnovich knocked out 2017 runner-up Alize Cornet of France 3-6, 6-2, 6-3, while Sevastova beat Aleksandra Krunic 6-2, 6-4.