Sixth seed Serena Williams has retired injured from her Wimbledon first-round match against Aliaksandra Sasnovich of Belarus.
The seven-times Wimbledon champion went off court for treatment while 3-2 up in the opening set but the American was in tears when she tried to resume and with the score at 3-3 could go no further.
The 39-year-old, who had been 3-1 up before the injury, sank to the grass sobbing, before being helped off the court.
Sasnovich, who practiced her serve while Williams was getting treatment, commiserated with an opponent who had never gone out in the first round at Wimbledon in her previous 19 visits.
"I'm so sad for Serena, she's a great champion," said the world No.100. "It happens sometimes."
Eight-times men's singles champion Roger Federer expressed shock at Williams' departure and voiced concern about the surface, with the roof closed on Centre Court on a rainy afternoon.
His first-round opponent Adrian Mannarino of France also retired with a knee injury after a slip.
"I do feel it feels a tad more slippery maybe under the roof. I don't know if it's just a gut feeling. You do have to move very, very carefully out there. If you push too hard in the wrong moments, you do go down," Federer said.
"I feel for a lot of players, it's super key to get through those first two rounds because the grass is more slippery, it is more soft.
"As the tournament progresses, usually it gets harder and easier to move on."
Earlier, Five-times champion Venus Williams, playing as a wildcard in her 23rd Wimbledon, showed vintage form to beat Romania's Mihaela Buzarnescu 7-5 4-6 6-3 and reach the second round.
The oldest woman in the draw at 41, Williams had not won a match since reaching the second round at the Australian Open in February, but showed she was far from finished on her return to a favourite place.
The Court Three clash of veterans, one of several held over due to rain on Tuesday (NZ time), was the 271st victory of a remarkable Grand Slam career for Williams and, despite serving 10 aces, did not come easy.
The American had powered to a 5-1 lead in the final set but then wobbled as Buzarnescu, 33, saved a match point and came back to 5-3.
The Romanian failed to convert three break points in the final game, but saved another match point, before Williams made sure of victory at the third attempt.
Former champ coasts into second round
Former champion Angelique Kerber started slowly but drew on her vast experience to beat Wimbledon debutant Nina Stojanovic 6-4 6-3 under the roof on Court One.
World No.1 Ash Barty overcame a mid-match blip to beat Spaniard Carla Suarez Navarro 6-1 6-7(1) 6-1 on Centre Court and advance to the second round.
Suarez Navarro, who returned to competitive tennis at the French Open after overcoming cancer, is set to retire after the Olympics. The 32-year-old received a standing ovation from the crowd as she left the court.
Former world No.2 and 2010 finalist Vera Zvonareva also advanced with her first Wimbledon main-draw win since 2014, defeating Marie Bouzkova 7-5 6-4. She faces Iga Swiatek next.
Former world No.1 Karolina Pliskova began her quest for a maiden Grand Slam title with a 7-5 6-4 victory over Slovenia's Tamara Zidansek.
The Czech eighth seed was joined in the second round by Ons Jabeur, who beat Rebecca Peterson 6-2 6-1.
Greece's Maria Sakkari, returning to action for the first time since her French Open semi-final defeat, powered past Aranxta Rus of the Netherlands 6-1 6-1 in 49 minutes.