A shock withdrawal by a "heartbroken" Aryna Sabalenka has thrown the women's draw into chaos, as Naomi Osaka won her first match at the All England Club in six years, while Casper Ruud gave a chilling insight into his battle with parasites. 

Here are the five quick hits from the opening day at Wimbledon.

1. Aryna Sabalenka's shock withdrawal throws women's draw into chaos

Wimbledon favourite Aryna Sabalenka has withdrawn before the tournament began due to an injured shoulder.

The two-time Australian Open champion was seeded third at the All England Club and was supposed to play Emina Bektas of the United States in the first round on Day 1 at the grass-court grand slam.

"Heartbroken to have to tell you all that I won't be able to play The Championships this year. I tried everything to get myself ready but unfortunately my shoulder is not cooperating," Sabalenka wrote on social media. 

"I pushed myself to the limit in practice today to try my best, but my team explained that playing would only make things much worse. This tournament means so much to me and I promise I'll be back stronger than ever next year."

Sabalenka was favoured to win the women's championship at Wimbledon, according to BetMGM Sportsbook.

A semifinalist at the All England Club in both of her past two appearances, Sabalenka was replaced in the draw on Monday by Erika Andreeva, who lost in qualifying last week. Andreeva ended up moving into the second round with a 7-6 (7-5), 3-6, 6-3 win over Bektas.

A little more than a week ago, Sabalenka stopped playing during the first set of her quarterfinal at the Berlin Ladies Open, citing pain in her shoulder.

She said she had a muscle injury that she called "very frustrating".

"The most annoying thing is that I can do anything. I can practice; I can hit my groundstrokes. I'm struggling with serving. That's really annoying. You don't feel like you're injured," Sabalenka said. 

"If you give me some weights, I'm going to go lift some weights. But if you tell me to serve, I'm going to go through pain. We did an MRI, we did everything. We did a lot of rehab, a lot of treatments and everything."

Her departure from the bracket on Monday without playing a point made Sabalenka one of several players who pulled out of the tournament just as it was beginning.

Ekaterina Alexandrova, who was the No.22 seed, withdrew because of an unspecified illness, hours before she was due to face 2021 US Open champion Emma Raducanu at Centre Court. Alexandrova's fill-in, Renata Zarazua, lost to Raducanu 7-6 (7-0), 6-3.

Victoria Azarenka, like Sabalenka a two-time Australian Open champion and former No.1, pulled out with a shoulder injury. The woman who replaced her, Elsa Jacquemot, was eliminated 6-3, 6-3 by 2017 US Open champion Sloane Stephens.

2. Naomi Osaka ends six-year Wimbledon drought

Naomi Osaka had not won a match at Wimbledon in six years. Hadn't even played there in five. Grass courts never were her favourite surface.

Twelve months ago at this time, Osaka was off the tour while becoming a mother — her daughter, Shai, turns 1 on Tuesday — and recalls flipping on the TV in the hospital and seeing a certain grand slam event on the screen.

"I'm just really excited to be here," Osaka said on Monday after pulling out a 6-1, 1-6, 6-4 victory over Diane Parry in the first round at the All England Club by taking the last two games from 4-all in the third set. 

"I know that I didn't play bad. I think I just put too much pressure on myself that I need to win all the games — that I can't be broken and things like that. 

"When that eventually happened, I felt like I doubted myself, even though I knew my game plan going in. So that's kind of what I just did in the third set."

Osaka has won the US Open and Australian Open twice apiece on hard courts, but never has been past the third round on either Wimbledon's grass or the French Open's clay. Osaka had not entered Wimbledon since a first-round loss in 2019, and while she's topped the WTA in the past, she is now No.113 in the rankings after being off the tour for 15 months until returning in January.

Before facing the 53rd-ranked Parry, Osaka said, she was sifting through pictures on her phone.

"They have that feature, 'This time last year.' I was looking at that. I was looking at photos of myself in the hospital. It's really cool to be here now," Osaka said. 

"My mindset last year was just trying to survive. Honestly, I didn't really know what was going on after I gave birth; just trying to piece myself back together."

3. Casper Ruud reveals battle with parasites after beating Aussie

No.8 seed Casper Ruud was made to work hard by Australian qualifier Alex Bolt 7-6 (7-2), 6-4, 6-4, and then relayed how a food bug had derailed both his French Open campaign and his Wimbledon preparation.

The 25-year-old Norwegian's bid struggled to deal with what was then an unknown stomach issue in Paris as he lost to Alexander Zverev.

"I went home the day after [losing at Roland Garros] and kept feeling quite bad for a full week … lying in bed all the time. I had no appetite," Ruud said.

"I took some tests and found out that I had this kind of uncommon small parasite that I had been infected with through not sure where. The most normal place where you can get infected from it is through unclean water.

"It is most likely like vegetable, fruit, or salad being washed with unclean water. It can take up to 12 days before it kicks in and you feel symptoms, so it's very difficult to know where I got it."

Ruud had been to Spain, Italy and Switzerland before Roland Garros and has no idea where and how he ended up getting the ailment.

"I did think if this keeps on going on for too long, Wimbledon might be at risk," he added. 

"I didn't have any appetite. I had very low energy and slept a lot and was just in bed pretty much the whole time."

4. Carlos Alcaraz's Wimbledon defence off to a perfect start after early jitters

Reigning Wimbledon men's champion Carlos Alcaraz began his title defence feeling a bit jittery, he said afterward, but came through with a 7-6 (3), 7-5, 6-2 victory over Estonian qualifier Mark Lajal.

"Stepping on this court, it's the most beautiful court I've played on. I still get nerves when I'm playing here," he said.

"I played for 45 minutes here on Thursday and it's the first time I get nervous practising. I'm glad, and I'm a privileged guy to play on this court.

"When I walk around, I get goosebumps. I remember last year and that was a great feeling."

Lajal, who is a week younger, was making his grand slam debut and felt it to his core, too.

"Two days before, I felt like I was going to throw up, I was so stressed," said Lajal, who actually went up a break in each of the first two sets. 

"When I found out who I was playing, and where I was playing, I was super excited. But as it sunk in — what I would be doing and who I was going to be playing — I was stressed about playing in front of such a huge crowd on one of the biggest stages in tennis."

Alcaraz will face Australia's Aleksandar Vukic in the second round after Vukic was one of three Australians to advance into the second round of the tournament on the opening day.

5. Thanasi Kokkinakis makes big admission ahead of Wimbledon opener

Thanasi Kokkinakis is not afraid to admit he's a bit like Bambi on ice when it comes to grass court tennis ahead of his first-round meeting with Canadian No.17 seed Felix Auger-Aliassime.

"Are you tentative when you play on grass?" he was asked the other day. 

"Yep," came the immediate, unhesitating response, without a flicker of a smile.

The big Australian's feeling of insecurity on the surface is something that's bugged him ever since he slipped on a wet court two years ago at a Challenger tournament in Surbiton and sprained the MCL in his knee.

And all the old demons came to haunt Kokkinakis at Queen's Club again a fortnight ago when he suffered another tumble and a similar MCL problem in his left knee that kept him out of action for a week to interrupt his preparations for Wimbledon.

But now he's at SW19, Kokkinakis, who had an eventful run to the third round on the clay at Roland Garros, is having to bury any negative thoughts as he prepares for an opening-round clash with Auger-Aliassime on Tuesday.

"I have been rehabbing to try and get as close as I can to 100 per cent. I'm getting close, having played an exhibition match last week, and hopefully I'm in good shape come Tuesday," said Adelaide's world No.93.

"The grass can be so dangerous. I got injured two years ago and I missed a month playing, so I've just got to be careful. At Wimbledon, more than anything, it's just trying to get to the start line healthy.

"Of course, I would have loved to have few matches and a bit more prep, but I'll just see what I can do.

"I think getting the confidence for me in moving is probably the biggest thing. That's the toughest part about a grass court. It's just trying to gain confidence in practice, trying to simulate as close to match conditions as I can.

"Playing an exhibition match is cool, but you don't want to injure yourself there and it's not the same intensity. So trying to get my head in the mindset of approaching it like I would at Wimbledon has been the most important thing."

AAP/AP