Two-time Wimbledon runner-up Ons Jabeur retired due to breathing difficulties after being in tears during her first-round match against Viktoriya Tomova.
The 30-year-old, who has endured a torrid time with injuries, required a medical timeout in the first set of the contest on Court 14.
Having been in clear distress, she managed to play on in scorching temperatures before withdrawing while trailing 7-6 (5) 2-0 to Bulgarian world number 111 Tomova.
Jabeur, who was beaten in the 2022 and 2023 finals at SW19, has plummeted to 59 in the rankings amid ongoing fitness setbacks.
A shoulder issue led to a premature end to her 2024 season and, just three months into her return, she hobbled off court in tears at this year's Miami Open after suffering a leg strain.
Tournament organisers later confirmed the Tunisian had experienced breathing issues.
"I wasn't expecting not to feel good, I've been practising pretty well the last few days but I guess these things happen and I'm pretty sad," said Jabeur.
"It doesn't really help me with my confidence. I keep pushing myself, even though it was a very tough season for me, so I hope I can feel better and see what's going to happen."
World number one Aryna Sabalenka (above) eased into the second round by defeating Canadian grand slam debutant Carson Branstine in straight sets.
The three-time major winner cruised through the opening set on Court One before securing a decisive break in game 11 of a closer second en route to a 6-1 7-5 success.
Belarusian Sabalenka, who missed last year's championship due to a shoulder injury and has never been past the semi-finals, could meet British number one Emma Raducanu in round three.
"I'm super happy to be back, to be healthy and to compete at this beautiful tournament," she said in her on-court interview.
"I was really depressed last year that I couldn't feel this atmosphere and I'm super happy with the performance. I feel like I'm in a good place."
Australian Open champion Madison Keys avoided an upset by coming from a set down to scrape past Elena-Gabriela Ruse.
The 30-year-old American sixth seed prevailed 6-7 (4) 7-5 7-5.
Katie Boulter registered one of the biggest wins of her career to join the rest of the Brit Pack in the second round.
The British number two sank Spanish ninth seed Paula Badosa 6-2 3-6 6-4 on Centre Court for only her fourth win over a top-10 player, and her first in more than a year.
She said: "I think I got one of my first against (Karolina) Pliskova on this court and the moment I stepped out here it just reminded me of that from the first ball.
"I just felt like I had some really good juju going on there and played some really good stuff, I'm happy to be through to the next round."
It meant seven heaven for Britain with Boulter and six other home stars through to round two, the highest total in a single day in the open era.
It was also sweet revenge for Boulter, who lost in three sets to Badosa in their only other meeting, at the French Open last year.
Emma Raducanu avoided an upset against 17-year-old Briton Mimi Xu as the British number one raced through in straight sets.
