Iga Swiatek was forced to retire in the third round of the Madrid Open on Saturday due to a viral illness, while reigning champion Aryna Sabalenka extended her winning run to 14 matches.
A champion in the Spanish capital in 2024, Swiatek rebounded from a one-set deficit against American 31st seed Ann Li to level the contest but put an end to proceedings while down 0-3 in the decider.
The Polish six-time Grand Slam champion asked for the doctor after getting broken early in the third set and got her vitals checked.
She tried to break Li back but when her opponent held for a 3-0 advantage, the fourth seed realised she was unable to continue.
She revealed after the match that she has been fighting a stomach virus for the last two days and was hoping she could still find a way to win despite feeling "terrible".
"I heard there is something going on between players, that the virus is somewhere on site. I'm sure I'll be fine in a couple of days, but I had zero energy and zero stability and just felt really bad physically, and yesterday even worse," said Swiatek.
It is Swiatek's earliest ever exit in five appearances in Madrid.
"On the court before the tournament I felt like I'm playing great, so actually it's sad for me that I can't play, because I was feeling really good with my game, and I was moving forward in the process, so, this was positive," she said. "But for me the tournament has just started and I couldn't even compete today, so it's disappointing."
Meanwhile, Sabalenka surged into the last 16 with a smooth 6-1, 6-4 victory against Romania's Jaqueline Cristian, who told her at the net she was "too good" and that she hopes the world number one would go on and win the tournament.
Sabalenka played a near-flawless opening set, winning 89 percent of her points on serve.
Cristian put up a bigger fight in the second set but Sabalenka got the decisive break in the ninth game en route to a convincing win.
The three-time Madrid champion, who next plays ex-world number one Naomi Osaka or Ukrainian qualifier Anhelina Kalinina, is known for her power game but she showcased some flair against Cristian, pulling off a running one-handed backhand passing shot in the first set and finishing the contest with a cunning drop shot winner.
"Especially in the first set, that was an incredible level from me. I even hit a one-handed backhand, which is a little bit crazy," said the four-time major winner. "I think that was the shot of my life, that's for sure."
Earlier in the day, 15th-seeded Iva Jovic squandered a lead and fell 3-6, 6-3, 6-2 to Canadian 24th seed Leylah Fernandez, who will be Li's opponent in the last 16.
WINS FOR ANDREEVA, ZVEREV
Ninth-seeded Russian Mirra Andreeva overcame an inspired Dalma Galfi 6-3, 6-2 in a match that was much closer than the scoreline suggested.
The Hungarian qualifier ranked 117 in the world broke early in both sets but was unable to maintain her advantage as Andreeva recovered to improve her clay-court record this season to 9-1 and set up a last-16 showdown with another Hungarian, Anna Bondar.
In ATP action, defending champion Casper Ruud raced into the third round with a 6-0, 6-1 demolition of home favourite Jaume Munar.
The 12th-seeded Norwegian will next take on Spain's Alejandro Davidovich Fokina.
Second-seeded Alexander Zverev recovered from a "terrible" second set to begin his campaign with a 6-1, 3-6, 6-3 performance against recent Bucharest champion Mariano Navone.
"First set was almost perfect, and then I lost focus completely, and then the second set was terrible," admitted Zverev, who previously clinched the trophy in Madrid in 2018 and 2021.
"But that's what happens sometimes, first match of a tournament. I definitely have to focus a bit better, but the level was there."
Zverev will next square off with Terence Atmane, who overcame excruciating cramps to triumph in an all-French duel 7-6 (7/3), 7-6 (7/5) over 30th seed Ugo Humbert.