Serena Williams tasted bitter defeat on her return to singles tennis at Wimbledon on Tuesday as Rafael Nadal overcame a huge scare to progress to the second round.
Elsewhere on day two of the Championships, title contender Matteo Berrettini was forced to pull out with coronavirus while women's top seed Iga Swiatek extended her winning streak to 36 matches.
Williams, 40, won the last of her Wimbledon singles titles six years ago but reached the final in 2018 and 2019.
Williams was far below her imperious best on Tuesday, struggling from the start with her form and fitness.
But she faltered while serving for the match and faded badly in the third-set tie-break after taking a 4-0 lead.
Earlier, an off-key Nadal, already halfway to a calendar Grand Slam after winning the Australian Open and French Open, dug deep to beat Francisco Cerundolo 6-4, 6-3, 3-6, 6-4.
"It's not a surface that we play very often, and especially in my case, for different reasons, the past three years I didn't put any foot on a grass court, so it always takes a while," said Nadal, 36.
The Spaniard appeared to be coasting to victory when he took a two-set lead but his Argentine opponent found a new level, winning the third set and going a break up early in the fourth.
The 22-time Grand Slam champion played the entire French Open with his troublesome left foot anaesthetised but he has received treatment since then and was moving well on Tuesday.
The sixth seed lost 6-7 (5/7), 6-4, 7-6 (11/9), 7-6 (7/5), removing another potential obstacle in the path of Nadal, who next faces Lithuania's Ricardas Berankis.
- Covid strikes -
"I am heartbroken to announce that I need to withdraw from @wimbledon due to a positive COVID-19 test result," the 26-year-old Italian wrote on Instagram.
He is the second man to withdraw from Wimbledon with Covid in two days after 2017 runner-up Marin Cilic of Croatia also tested positive.
It is business as usual at the Grand Slam this year after the tournament was cancelled due to Covid in 2020 and last year was played in front of reduced crowds.
Poland's world number one Swiatek, who has won her past six tournaments -- coasted into the second round with a routine 6-0, 6-3 victory against Croatian qualifier Jana Fett.
Beaten French Open finalist Coco Gauff, the 11th seed, recovered from losing the first set against Romania's Elena-Gabriela Ruse to win 2-6, 6-3, 7-5.