Day 9 of the BNP Paribas Open will see the completion of quarterfinal action and the semifinal lineup set. Reigning Grand Slam champions Iga Swiatek and Elena Rybakina both face unseeded opposition as they bid to join Aryna Sabalenka and Maria Sakkari in the last four.

More from Indian Wells: Scores | Order of play | The best of Week 1 | Cirstea's new outlook on tennis | Sabalenka sweeps past Gauff | Sakkari reels in Kvitova 

[1] Iga Swiatek (POL) vs. Sorana Cirstea (ROU)

Head-to-head: Swiatek leads 1-0

Ominously for the rest of the field in Indian Wells, Iga Swiatek is feeling herself this fortnight.

"I'm just playing better and better every match," she said after dispatching Emma Raducanu in the fourth round. "I'm ready for anything. I know that I can return really well, and if I'm gonna make it to the rally, I can make advantage there."

Twelve months ago, Swiatek had to come from a set down three times -- against Anhelina Kalinina, Clara Tauson and Angelique Kerber -- en route to the title. As defending champion this year, she has dropped 14 games in three matches so far, nine of those to Bianca Andreescu in the third round.

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No.83-ranked Sorana Cirstea is also learning to love the desert. In her first nine appearances at Indian Wells, the Romanian won just five matches. Last year she reached the fourth round for the first time. This year, facing the pressure of potentially dropping out of the Top 100 with the loss of those points, she's gone one better. Cirstea's win over Caroline Garcia was her first win over a Top 5 player since defeating Karolina Pliskova in the third round of Beijing 2017 -- which was also the last time she made a WTA 1000 quarterfinal.

Cirstea, 32, has been beyond the last eight at this level only once before, when she was the runner-up at Toronto 2013. She has the toughest task on tour when she goes up against Swiatek, but she'll be bolstered by taking the Pole to three sets in their only previous meeting. That was a significant one for Swiatek, who won 5-7, 6-3, 6-3 in the fourth round of the 2022 Australian Open to reach her first major quarterfinal on hard courts.

Karolina Muchova (CZE) vs. [10] Elena Rybakina (KAZ)

Head-to-head: Muchova leads 1-0

The last time Wimbledon champion Elena Rybakina and Karolina Muchova met came in the first round of the 2019 US Open. Rybakina was a 20-year-old qualifier ranked No.69. She was playing in just her ninth tour-level main draw, and fell 6-4, 6-4.

Now Rybakina has reached her second straight Indian Wells quarterfinal without dropping a set. She's improved as the fortnight has gone on, dropping fewer games in each successive round against Sofia Kenin, former champion Paula Badosa and Varvara Gracheva. Rybakina has been open about the slow conditions not being ideal for her power game, but key to her run has been a willingness to change.

"Conditions are not easy, but I'm trying to adapt with my game also," she said after beating Badosa.

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Muchova rarely has trouble switching things up, and the 26-year-old has now reached her second WTA 1000 quarterfinal in a row following Dubai last month. She's come through a stacked draw the hard way, needing three-setters to defeat Yulia Putintseva, Martina Trevisan and Marketa Vondrousova. Ironically, her only straight-sets win so far was over two-time champion Victoria Azarenka in the second round.

Former World No.19 Muchova seems to be perennially on the comeback trail from injury. Abdominal and back issues beset her in 2022, but her ranking is back at No.76 after slipping out of the Top 200 last summer. Still, she has to play it safer than most.

"The injuries that I had are coming back a little bit, so we have to be cautious," Muchova said after defeating Azarenka. In Dubai, her abdominal injury forced her to withdraw ahead of the quarterfinals. A healthy Muchova against Rybakina should, however, make for an intriguing stylistic contrast.