The quarterfinal lineup at the Credit One Charleston Open was completed on Thursday with wins by three of the top four seeds -- and one big upset from Anna Kalinskaya over Australian Open champion Madison Keys.

Kalinskaya was a 6-2, 6-4 winner against No. 2 seed Keys in the first match of the night session inside Credit One Stadium, taking advantage of an erratic performance by the World No. 5 to score her first Top 10 victory in 10 months and advance to her second quarterfinal of the season. Keys hit 40 unforced errors in defeat, won less than 50% of points on her first serve, and converted just one of eight break point opportunities -- all of which combined to help Kalinskaya level her all-time head-to-head record against Keys to 1-1. 

Charleston: Draws | Scores | Order of play

But Kalinskaya's win over Keys wasn't the only upset on paper in the Round of 16. Read on for more top stories from Thursday in Charleston.

Kalinskaya 'needed this' amidst rough start: Kalinskaya, who peaked at a career-high ranking of No. 11 last October on the back of a 2024 season that saw her reach a WTA 1000 final in Dubai, a WTA 500 final in Berlin, and the second week of two Grand Slam events hadn't yet recaptured that form in the first three months of 2025. After missing the Australian Open due to illness, she entered Charleston at 4-7 on the season and having won back-to-back matches at just one tournament, in Singapore in February (where she retired in the semifinals). 

But after securing an 11th career Top 10 win against Keys, the 26-year-old said the result was one she "needed."

Must See

"This one is special. I needed this for my confidence. I had an unfortunate start to the year, but it's nice to be back and playing at such a high level," she said. "I think the key tonight was to change a little bit the rhythm; I did a few drop shots, especially in the first set.

"I didn't want to go into very long rallies, because she's a great player and she has unbelievable strong shots, so I tried to step in on the serve, be aggressive as much as I could, and be very consistent ... to keep the level, and I think that was the key."

Kalinskaya will next face 2020 Australian Open champion Sofia Kenin, who upset No. 5 seed Daria Kastkina in the nightcap, 6-3, 7-6(7).

Pegula keeps coasting: While her other top seeds have struggled in the first two rounds, there has been no such dram for No. 1 seed Pegula. After losing three games in her first round, Pegula lost just five against Ajla Tomljanovic to book a spot in her fifth quarterfinal of the season, 6-3, 6-2. 

The match was a far cry from the 6-1, 4-6, 6-3 semifinal that the two played in Austin last month, with Pegula winning five straight games in the middle of the match to pull away. 

She'll take a perfect 5-0 head-to-head record against her next opponent, defending champion Danielle Collins, into the quarterfinals. Collins came from a break down in both sets to defeat No. 11 seed Jelena Ostapenko 7-5, 6-3 and win her eighth straight match in Charleston.

Zheng survives, Alexandrova tops Shnaider: Olympic champion Zheng Qinwen's 13th consecutive clay-court win, meanwhile, didn't come as easily. The No. 3 seed was forced to come from a break down in the final set en route to defeating No. 13 seed Elise Mertens, 6-3, 3-6, 6-3. 

She will next face No. 9 seed Ekaterina Alexandrova, who was a 6-1, 6-2 winner against No. 6 seed Diana Shnaider. Linz champion Alexandrova's two wins this week snapped a four-match skid -- which followed eight consecutive wins -- dating back to the semifinals of the Qatar Total Open in February.