French Open champion Iga Swiatek is through to the semi-finals of the Adelaide International after Ash Barty’s conqueror was forced to pull out with injury.

World No. 18 Swiatek was leading 6-2, 3-0 when American Danielle Collins retired during Thursday’s quarterfinal.

Collins, who beat world No. 1 Barty in straight sets a day earlier, took a medical timeout to address the issue, but she was only able to play three more points upon her return before calling it quits.

The exact nature of Collins’ injury was unclear, but she winced in pain during her service action in the final point before retiring.

Iga Swiatek of Poland celebrates winning a point against Danielle Collins. Sarah Reed/Getty Images

“Unfortunately we couldn’t finish … Hopefully Danielle is going to be well soon,” Swiatek said during her on-court interview after the match.

“Even though she wasn’t in her best shape today, I played very good tennis and I felt very confident, and that’s the most important thing for me.”

Collins committed 16 unforced errors to five in the opening set, with the wayward display easing the pressure on Poland’s Swiatek.

The second set was all one-way traffic before Collins pulled out with injury.

Earlier in the day, Swiss Jil Teichmann and American teen Coco Gauff secured spots in the final four after surviving tough quarter-final encounters.

Teichmann clawed her way to a marathon victory over Latvian veteran Anastasija Sevastova, winning 6-4, 6-7(8), 7-5 and will take on Swiatek.

They were later joined by Gauff, who also had a fighting battle with fellow American Shelby Rogers.

Recovering from a patchy start, the 16-year-old Gauff triumphed 2-6, 6-4, 6-4.

She’ll play the winner of the Storm Sanders-Belinda Bencic match.

Teichmann had five match points in the second-set tiebreaker but was unable to close it out.

The 23-year-old was then forced to save two match points while trailing 5-4 in the third.

Teichmann levelled at 5-5 before breaking Sevastova’s serve and finally secured the rollercoaster victory on her seventh match point, taking just under three hours.

The world No. 61 led 6-3 in the tiebreak but she couldn’t shake her opponent, who squared it at 6-6.

The young Swiss had a further two chances, netting her fifth match point, while world No. 56 Sevastova made no mistake with her first opportunity to push the match to a deciding set.

Teichmann looked down and out early in the third, trailing 3-0, but she showed bravery to keep going for her shots, with her booming forehand doing most of the damage.

“It was a rollercoaster and what I felt was nerves,” Teichmann said.

“It was a very tense match, very long rallies every time and Anastasija is a tough player and you have to play every point and every game, doesn’t matter if you’re serving or returning.”