Jessica Pegula dethroned reigning champion Danielle Collins, as she came from behind to book her place in the Charleston Open semi-finals.

The top seed recovered from a set and a break down to prevail 1-6 6-3 6-0 after one hour and 44 minutes, and set up a last-four clash with Ekaterina Alexandrova.

Collins came flying out of the blocks, hitting 12 winners as she raced through the opening set in just 27 minutes.

The defending champion then broke early in the second set and held three game points for a 3-1 lead, but could not convert any with Pegula recovering to break back.

That swung the contest completely in her favour, as she reeled off 10 of the next 11 games to make it seven straight victories over Collins, while reaching her third successive semi-final in Charleston.

"She came out just firing, and I was not ready for that at all," Pegula said in her on-court interview.

"Luckily, somehow, I was able to dig my heels into that second set and play some good tennis.

"I don't even know if I got fired up. I just felt relieved when she missed a couple of balls. I tried to mix it up when I could, throw in some slices and drop shots.

The fantastic four in Charleston#CharlestonOpen pic.twitter.com/axS7FyNnkF

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"Her backhand is one of the best backhands on tour, so I was like: 'Stop hitting to her backhand as much - that would probably help'.

"She was returning unbelievable, just hitting winner, winner, winner off my serve, and I had to figure out a way to get my placement a little bit better."

Next up for her will be Alexandrova, who was a 6-1 6-4 winner over third seed Qinwen Zheng.

The ninth seed converted three of five break-point opportunities, while saving all three she faced, to progress to her third semi-final of 2025.

However, there was no joy for hometown favourite Emma Navarro as she was defeated 7-5 7-6 by Amanda Anisimova.

The latter will take on Sofia Kenin, who was also a straight-sets winner over Anna Kalinskaya, meaning there will be three American semi-finalists at this event for the first time since 2003.