Filipino star Alexandra Eala moved into the last 16 at Indian Wells after world No 4 Coco Gauff was forced to retire from their match on Sunday evening.
After losing the first set 6-2, two-time major champion Gauff trailed 2-0 in the second set before retiring due to persistent pain in her left arm, which she said made it feel like it was "on fire".
Gauff, 21, who has only retired from one match previously in her career, took a medical timeout before the final game and apologised to Eala.
"I'm sorry. You were playing great," Gauff told Eala as they embraced at the net.
"I really didn't want to win this way," world No 32 Eala said after the match. "But this is still a really big moment for me to be able to play on Stadium 1 at Indian Wells, against such a great competitor."
It was a tough break for American Gauff, who crushed Eala 6-0, 6-2 in the quarter-finals at the Dubai Duty Free Tennis Championships three weeks ago and was among the favourites to win the title in the California desert. Gauff's only other retirement came in 2022 in Cincinnati.
"It felt like a firework was going off inside of my arm, and then my whole arm felt like it was on fire," Gauff said after the match.
"We're going to figure out what it is tomorrow, but based off the feeling, I'm being told that it's probably something nerve-related."
She said she would get an MRI on Monday to assess the situation.
"The good news is they don't think it's going to be a long-term type of situation, so I should be fine for Miami," she said, referring to the second leg of the Sunshine Double that takes place immediately after Indian Wells.
"We've just got to figure out exactly what it is and, I guess, how to prevent it in the future."
Eala, 20, who has become a celebrity in the Philippines with wins over some of the sport's biggest names, will next face Czech Linda Noskova for a place in the quarter-finals.
"It's a difficult decision to retire from a match, I know," Eala said. "No one likes winning like that and no one likes losing like that. Nevertheless I'm really happy with how I played, really happy with my performance and I hope I can make the best out of the momentum."
Eala's first match, on Stadium 3 on Friday, was packed. The line to get to the general admission seating was more than 100 people long midway through the match.
On Sunday, Eala spent much of her post-match interview on the court thanking her parents and those who've helped her get to this point in her career so far.
"I do my best to be humble and to keep my feet on the ground because I am surrounded by so many amazing players," she said. "Tennis is a really humbling sport because you really learn how to lose and learn to be self-aware."
