Naomi Osaka began the defence of her Pan Pacific Open crown with a quick win after opponent Daria Saville was forced to retire in just the second game.

Four-time grand slam champion Osaka won the opening game, before Saville was unable to continue due to a scary-looking injury to her left knee.

The former world number one will now face a second round match with world number 16 Beatriz Haddad Maia, who eased to a straight sets victory over Yuki Naito.

Karolina Pliskova secured her place in the next round in Tokyo with a 6-2 6-1 demolition of Isabella Shinikova, while Zhang Shuai will face second seed Caroline Garcia on Wednesday after overcoming Mai Hontama in two sets.

In Seoul, Jelena Ostapenko's hopes of repeating her 2017 heroics at the Korea Open are still alive after the number one seed narrowly beat 19-year-old Jeong Bo-young.

The world number 19 looked to be cruising after the opening set, but the unheralded South Korean hit back in the second and took it to a tie-break in the third, before Ostapenko's class showed as she won the crucial tie-break 7-2.

Elsewhere, 2021's beaten finalist Kristina Mladenovic saw off wildcard Park So-hyun 6-4 4-6 6-3, while second seed Ekaterina Alexandrova overcame a worrying second set to beat Asia Muhammad 6-1 3-6 6-1.

Wimbledon semi-finalist Tatjana Maria is also safely through to the second round after a tight 7-6 (7-5) 7-6 (7-5) triumph over Eugenie Bouchard.

Naomi Osaka pulled out of Wimbledon on Saturday as tournament officials said the former world number one was suffering with a leg injury.

The announcement came in the wake of Osaka revealing she was considering skipping the grand slam in any case, as she suspected it may feel "like an exhibition".

The All England Club's decision to ban Russian and Belarusian players from competing has resulted in the WTA and ATP stripping Wimbledon of all ranking points.

Osaka, who is a four-time grand slam champion, suggested after her first-round exit at the French Open that she was unsure about whether to commit to the grass-court major.

Confirmation of her absence from the event, which starts on June 27, came from Wimbledon as her name was added to a list of withdrawals.

The Japanese 24-year-old has only played Wimbledon's main draw three times in her career, twice reaching the third round. She has yet to go further but has won the Australian Open twice and the US Open on two occasions. Recently she complained of a "stubborn" Achilles problem.

Osaka was joined on the withdrawal list by Eugenie Bouchard, the 28-year-old Canadian who was runner-up to Petra Kvitova at the 2014 Wimbledon championships.

Wimbledon listed Bouchard as absent due to a shoulder problem; however, that told only part of the story.

She is battling her way back up the rankings after injury and disappointing results and said she could not risk using a special entry dispensation on a tournament that will carry no points.

Bouchard wrote on Instagram: "I have decided to withdraw from Wimbledon due to the WTA's decision to not award ranking points at this year's championships.

"Due to my shoulder surgery, I get a limited number of protected ranking [PR] entries. As much as I love Wimbledon and skipping it makes me sad, using a PR entry at a tournament with no ranking points doesn't make sense. I must choose wisely and use my PR at tournaments that will help me get back to where I want to be."

She said she would use her protected ranking grand slam entries for the next US Open and Australian Open.

Iga Swiatek continued her outstanding form as she cruised into the French Open semi-finals with a 6-3 6-2 win over Jessica Pegula, joining an elite list of young players to have reached the final four in the year's first two grand slams.

In racking up her 33rd consecutive win, the world number one ensured she followed up her semi-final appearance at this year's Australian Open with another deep run at Roland Garros.

On the day after her 21st birthday, 2020 French Open champion Swiatek joined a select group of players in managing that feat, with only six women making back-to-back semi-finals at the tournaments at a younger age than the Pole since the turn of the century.

They are Martina Hingis, Justine Henin, Kim Clijsters, Ana Ivanovic, Eugenie Bouchard and Maria Sharapova.

Having become just the fourth woman this century to win five consecutive tournaments on the WTA Tour coming into Roland Garros, Swiatek will go into her semi-final clash against Daria Kasatkina confident of taking another step towards a second grand slam title.

Former US Open champion Sloane Stephens has continued her torrid start to 2021 after crashing out in the first round of the Monterrey Open on Tuesday.

Stephens went into the Mexico event as top seed but lost to Slovakian world number 151 Kristina Kucova 6-2 6-2.

The 27-year-old American is now 0-4 to start the 2021 WTA Tour season and has won only one set all season.

Stephens, now ranked 48th in the world, only managed to win 32.4 per cent of points on her first serve, with Kucova converting seven of 14 break points in the match.

Second seed Nadia Podoroska was also a first-round casualty on Tuesday, going down 6-4 6-4 to Russian qualifier Anna Kalinskaya.

In the late match, Eugenie Bouchard went down to China's Lin Zhu 7-5 7-6 (6-3).

Madison Keys is intent on giving Maria Sakkari a second-round test after marking her first WTA Tour appearance since September with a clinical win at the Qatar Open.

American world number 19 Keys, who reached the US Open final in 2017, had not played on tour since losing to Zhang Shuai in the first round of the French Open in late September – she was ruled out of the Australian swing of this season after a positive coronavirus test.

But Keys roared back to action with a thumping 6-4 6-1 victory over Belinda Bencic on Tuesday, the Swiss who last week reached the Adelaide International final.

"I'm really happy with how I came out and played today," Keys said. "I'm a little bit surprised with myself but hoping to keep the momentum going."

Sakkari promises to pose a tricky test for Keys, who is unseeded this week, given the Greek player dropped only three games in her opening win over Mayar Sherif and has shown bright early-season form.

World number 23 Elena Rybakina tripped up in the first round after the Moscow-born Kazakh player lost 7-6 (9-7) 7-6 (7-5) to Germany's 56th-ranked Laura Siegemund at the WTA Premier event.

Jessie Pegula, Anastasia Pavlyuchenkova, Ons Jabeur and Misaki Doi also scored straight-sets victories in Doha.

At the Lyon Open, French players Caroline Garcia and Kristina Mladenovic were both pushed to three sets before inking their places in the last 16.

Third seed Garcia edged compatriot Oceane Dodin 6-2 2-6 6-3, while fourth seed Mladenovic scrambled for a 5-7 7-5 6-2 win over Romanian Mihaela Buzarnescu.

Former Wimbledon runner-up Eugenie Bouchard, in on a wildcard, was bounced out 7-6 (9-7) 6-2 by Aliaksandra Sasnovich, the world number 96 from Belarus.

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