Iga Swiatek reached the Adelaide International semifinals Thursday after Danielle Collins retired with a lower back injury trailing 6-2, 3-0.

The No. 5 seed Swiatek displayed some brilliant tennis to keep Collins at bay until the American pulled out. Swiatek, who reached her third career WTA semifinal, fired 17 winners, won all 10 points on Collins' second serve and kept her unforced error count to just four in the first set. Swiatek would also came out on top of a trio of three-deuce tussles behind her own serve that had threatened to be turning points - holds for 3-0 and 5-2 in the first set, and 1-0 in the second. 

The Pole's defensive skills were also on full display in one of the best exchanges of the tournament: Swiatek's deft hands at full stretch to conjure pinpoint lobs were reminiscent of compatriot Agnieszka Radwanska, as was her tactical acumen in ghosting into net to snatch a point that had seemed a lost cause. One game later, Collins would call it quits after an off-court medical timeout.

Afterwards, Swiatek discussed how the Covid-19 pandemic has benefited her as she has settled into life as a Grand Slam champion.

"Quarantine in Australia was the first time I could chill out and not worry about everything that's been going on after the French Open."

- Iga Swiatek on one of the hidden benefits of the pandemic.

"I didn't see a lot of people around," she recalled of her return to Poland after Roland Garros. "Because at that time we had many restrictions and it was impossible to get big gatherings. So it was actually good that the pandemic is here, because it was really good for me - I could try to learn how to deal with it step by step. It's going to be probably different when the pandemic is over, but I have this experience now."

Arriving in Australia, quarantine also enabled Swiatek to take a breather.

"The first three weeks [after Roland Garros] were pretty hectic, and I didn't play tennis at all because I had so many media obligations," she said. "It was the end of the season so I also had some holidays, but I didn't feel like I was actually resting during those holidays because my head was still focused on everything that was going around. Actually, I feel like the quarantine in Australia was the first time I could chill out and not worry about everything that's been going on after the French Open."

Earlier action had seen Jil Teichmann and Coco Gauff each pull off stellar comebacks to reach their first semifinals at WTA 500 level or above. World No.61 Teichmann seemed to have squandered her chance against Anastasija Sevastova after the Latvian saved five match points in the second-set tiebreak.

Gallery: Great Escapes 2021: Winning from match point down

The Swiss player held firm, though, facing down two against her while serving at 4-5 in the decider and ultimately capturing her seventh for a 6-4, 6-7(8), 7-5 victory after two hours and 57 minutes. Teichmann will now face Swiatek for a place in her fourth and biggest WTA final.

2021 Adelaide Highlights: Gauff comeback classic halts Rogers

Unlikely comebacks are familiar territory for Gauff, who has shown a precocious ability in her young career to adjust tactically and cling on mentally after getting initially outgunned. The 16-year-old qualifier recovered from 2-6, 2-4 down, as well as trailing 2-4 in the final set, to defeat Shelby Rogers 2-6, 6-4, 6-4 in one hour and 50 minutes. Of Gauff's 38 victories in WTA main draw and qualifying matches, 14 have been three-setters, and 10 of those have been comebacks after losing the first set.

A semifinal lineup featuring Gauff and Swiatek raises the possibility of the first all-teenage WTA 500 (previously Premier) final since Daria Kasatkina defeated Jelena Ostapenko to win Charleston 2017 when both players were 19 years old. Gauff's next opponent knows a thing or two about being a teenage prodigy, though. No.2 seed Belinda Bencic reached the US Open quarterfinals at 17 and won both Eastbourne and Toronto at 18, and booked her own last-four spot by defeating qualifier Storm Sanders 6-2, 6-4.

Despite the gulf in rankings and experience - World No.292 Sanders was playing her first ever WTA quarterfinal - the contest was a high-quality one. Bolstered by crowd support, the left-handed Sanders impressed with her touch at net and the raking angles she could create from both wings, and struck 21 winners to 25 unforced errors in total.

Bencic, who has been open about struggling to rediscover her best form in Australia following her hard quarantine experience, needed some clutch serving to stave off eight out of nine break points. The 23-year-old, who found 25 winners to 21 unforced errors, was also able to come with her best tennis in key moments.

In the second set, Bencic faced a resurgent Sanders, who had broken for the first time to level the score at 3-3. But she was able to scramble to win a thrilling point before breaking the Australian with a perfect volley - wresting back momentum that ultimately saw her over the finishing line.

With Bencic and Teichmann in opposite halves of the draw, the Adelaide last four also raises the possibility of the first all-Swiss WTA final in the Open Era.