Britain’s Francesca Jones said she had “no idea what just happened” after fighting through injury to reach the Auckland Classic quarter-finals.
Jones registered the biggest win of her career on Monday with a three-set victory over world number 15 Emma Navarro.
It looked as though the 25-year-old was feeling the after-effects when she went a set and a break down against Austrian qualifier Sinja Kraus, having twice called for the physiotherapist.
However, she regrouped and lost just two further games in a 1-6 6-4 6-1 victory.
“I’m actually really relieved that’s over,” Jones told Sky Sport in New Zealand.
“When you play someone like Emma in the first round and you get through that, physically and mentally it’s tough to pick yourself back up, especially in these conditions.
“I’m glad I got through that.”
British number three Jones broke into the top 100 last year, having won two WTA 125 titles – the rung below the main tour.
She was previously told by doctors she would not play tennis professionally, having been born with a rare genetic condition.
Jones has Ectrodactyly Ectodermal Dysplasia (EEC), which means she has three fingers and a thumb on each hand, three toes on her right foot and four toes on her left.
Jones struggled with the hot conditions in Auckland but battled back well, saving nine of the 13 break points she faced to advance in just over two hours.
“She was unplayable the first set and a half and I found it really tough to get used to playing in the day compared to the night. It’s a lot quicker,” Jones added.
Jones will play Chinese seventh seed Wang Xinyu for a place in the last four.
Elsewhere, Wimbledon champion Iga Swiatek helped Poland reach the quarter-finals of the United Cup mixed team competition.
World number two Swiatek was a swift 6-3 6-2 winner over Suzan Lamens of the Netherlands after Hubert Hurkacz beat Tallon Griekspoor 6-3 7-6 (7-4).
Poland will face hosts Australia on Friday.
