Naomi Osaka moved into the fourth round at the Miami Open without even taking the court on Saturday, getting a walkover victory as Karolina Muchova withdrew.

The former world number one claimed straights sets victories coming into Saturday and had her run eased even further, with Muchova citing abdominal injury after almost five hours on court in her opening two matches.

Muchova has been sidelined due to the injury for the last seven months, missing the US Open in 2021 as well as the Australian Open this year.

"I'm sad that I cannot put up a battle against Naomi today." Muchova tweeted. "After a long break from tennis, two tough matches in [a] row have been a lot for my body and I need longer to recover."

While Lucia Bronzetti also won in a walkover, Osaka will face Alison Riske, who defeated fellow unseeded American Ann Li 6-2 3-6 6-3.

In her third match since losing to Ash Barty in the Australian Open final, Danielle Collins defeated Vera Zvonareva 6-1 6-4 in 78 minutes.

The American world number 11 has had to deal with numerous niggling injuries this season, including a viral illness that left her with significant neck pain.

"There was obviously an emotional moment for me, the pain I'm dealing with right now with this injury," she said post-match.

"Just trying to work through that, I think is one of the hardest things we go through mentally when we're on court."

Fellow seeds Belinda Bencic and Ons Jabeur also made their way through to the fourth round, defeating Heather Watson and Kaia Kanepi respectively.

Both won with relative comfort, with Bencic winning 6-4 6-1, and Jabeur only dropping three games in the opening set to triumph 6-3 6-0.

World number one Ash Barty was relieved but happy with her response after surviving a first-round scare against Vera Zvonareva at the US Open.

Barty – the top seed back at Flushing Meadows after skipping the 2020 event due to the coronavirus pandemic – booked her spot in the second round with a 6-1 7-6 (9-7) victory but the Wimbledon champion endured a challenging opener in New York on Tuesday.

Despite firing down 11 aces to improve her WTA Tour-leading tally to 300 in 2021, and hitting 31 winners, veteran Zvonareva was a tricky first-up opponent for Australian star Barty.

A US Open and Wimbledon runner-up in 2010, Zvonareva made life difficult for Barty in the second set, earning a chance to force a decider but the 36-year-old was unable to capitalise at 7-6 in the tie-break.

Afterwards, Barty – who ranks first this season for titles (five), match victories (41), finals reached (six) and top-10 victories (seven) – told reporters: "Obviously a tough one against Vera straight up.

"She's an experienced campaigner. She knows how to get herself into matches. I think all in all, adapting to conditions was a little bit slower than I probably would have liked [but] we're through. We have another chance to improve on that in the next round.

"I think when my back was against the wall late in that buster, I came up with some really good stuff. That's all we can ask is when your back is against the wall, you trust yourself, you go out there and pick your spots and hit them."

Two-time grand slam champion Barty – fresh off winning in Cincinnati as Clara Tauson awaits in round two – added: "It obviously got really tense in that second set - tight - and in the bigger moments I was able to be aggressive and trust myself and that was a massive thing today.

"There were a couple of games where I had lapses in concentration but I was able to come through in straight sets and now we go back to the drawing board, work on a few things and we'll be as happy as Larry.

"I'm certainly happy to be through and playing again here in New York."

Stefanos Tsitsipas faces Andy Murray and Ash Barty will take on 2010 finalist Vera Zvonareva in the first round of the US Open.

French Open runner-up Tsitsipas and 2012 champion Murray is one of the standout matches in the opening round at Flushing Meadows.

Top seed Novak Djokovic will start his quest for a calendar Grand Slam against a qualifier in New York and could face a repeat of the Wimbledon final versus Matteo Berrettini in the last eight.

World number one Djokovic, a strong favourite for a record 21st major title with Rafael Nadal and Roger Federer absent due to injury, could do battle with Alexander Zverev at the semi-final stage.

Daniil Medvedev, the second seed, is in the bottom half with Tsitsipas, who he could come up against in the semi-final. Medvedev's first test will come against Frenchman Richard Gasquet.

Barty could come up against Iga Swiatek in the last eight and Karolina Pliskova if she makes it through to the semi-finals.

Simona Halep's encounter with Camila Giorgi is a mouthwatering first-round match, while defending champion Naomi Osaka returns to grand slam action against former US Open junior champion Marie Bouzkova.

Angelique Kerber could be a tough fourth round opponent for Osaka. Close friends Madison Keys and Sloane Stephens meet in another eye-catching first-round match.

There will be no Serena or Venus Williams at the final major of the year due to injuries.

Daria Kasatkina and Margarita Gasparyan fended off two of the great stalwarts of Russian tennis to set up a final showdown at the St Petersburg Ladies Trophy.

Kasatkina recovered from a slow start to overcome fourth seed and two-time grand slam winner Svetlana Kuznetsova, after Gasparyan saw off former Wimbledon and US Open runner-up Vera Zvonareva.

Zvonareva, 36, and Gasparyan, whose promising career has been disrupted by injury, were both allocated wildcard entries to the tournament and seized advantage to reach the last four.

Gasparyan, a 26-year-old whose single-handed backhand is an unusual sight in modern tennis, came through the clash with Zvonareva a 6-3 7-6 (11-9) winner to reach her first final at WTA 500 level.

The world number 126 will tackle former top-10 star Kasatkina for the title, after the 23-year-old Barcelona resident scored a remarkable 1-6 6-0 6-2 win over Kuznetsova in the second semi-final.

It was a flat Kasatkina who surrendered the opening set, but she then dashed off eight games in a row, levelling the match and surging to a 2-0 lead in the decider, knocking the stuffing out of 35-year-old Kuznetsova's challenge.

Kasatkina, a 23-year-old with more variety than most, had also dropped the first set 6-1 in her quarter-final win over second seed Veronika Kudermetova on Friday before finding her best game.

She said on Amazon Prime: "Well, why not, if losing the first set will guarantee me victory, why not?"

Kasatkina, the eighth seed this week, won the Phillip Island Trophy in Melbourne last month so is chasing a second WTA title of the year.

She is relishing the clash with Gasparyan, saying: "It's cool to have players of different styles. Tomorrow's a final so you've just got to go out there and try to show your best tennis."

An all-Russian final was already guaranteed, given the host country locked down all four semi-final places, and it will be the 30th such WTA title match.

Daria Kasatkina and wildcard Margarita Gasparyan sank the top two seeds at the St Petersburg Ladies Trophy, where the semi-finals will be all-Russian showdowns.

Ekaterina Alexandrova, the number one seed, fell 6-2 7-5 to Gasparyan, before former top-10 star Kasatkina continued her recent revival by landing a 1-6 6-1 6-2 victory against Veronika Kudermetova.

Friday marked the first time at a WTA tournament that as many as seven of the final eight players have been Russian, and the day's opening clash produced a significant upset.

It was a valid reminder of what might have been for world number 126 Gasparyan, who like Alexandrova is 26 years old but has struggled massively with injuries over the years.

Gasparyan was particularly helped by her superior form on first serve in the opening set, putting 72.7 per cent in court to 44 per cent by her opponent and winning 75 per cent of points when landing that delivery.

A topsy-turvy second set saw a total of seven breaks between the two players, but Gasparyan's 4-3 advantage in that respect helped her clinch a first WTA 500 semi-final appearance.

Up next for her is 36-year-old Vera Zvonareva, the former world number two who beat Anastasia Gasanova 6-3 6-1, saving six of seven break points en route to victory.

Romania's Jaqueline Cristian was the final non-Russian player left in the draw and she certainly tested Svetlana Kuznetsova, but ultimately the 35-year-old fourth seed prevailed 6-7 (5-7) 6-3 6-3.

Next for former US Open and French Open winner Kuznetsova will be Kasatkina, who rounded off the day by shaking off a slow start to look highly impressive against second seed Kudermetova.

The 23-year-old Kasatkina has endured a couple of lean years since entering the top 10 in October 2018 but landed a title last month at the Phillip Island Trophy.

Asked about how she came back from being trounced in the opening set by Kudermetova, Kasatkina said on Amazon Prime: "I think it's just women's tennis and this is what tennis is all about.

"It took me some time to get into this match but at the end I won it."

As for how Saturday's clash with Kuznetsova might play out, Kasatkina said: "We trained many times together but never played in an official match so it's hard to say."

Russian duo Svetlana Kuznetsova and Vera Zvonareva recorded contrasting victories on home soil to reach the last eight of the St. Petersburg Ladies Trophy.  

Kuznetsova - who has won both the French and US Open during her distinguished career - needed just over an hour to get past teenage qualifier Wang Xinyu by a 6-1 7-5 scoreline.  

The 35-year-old converted six of the nine break-point opportunities she created, though was made to work for her win in the second set having previously taken nine of the opening 10 games.  

After failing to serve out for the match when 5-3 ahead, the fourth seed eventually prevailed when recording a break of her own with the score at 6-5.  

Zvonareva, meanwhile, was on court for three hours and 10 minutes as she produced an impressive upset, knocking out third seed Fiona Ferro 6-7 (8-6) 7-5 7-6 (7-2).  

"We both were fighting for every point, trying to hang in there. I think I was able to play some good tennis when it mattered, and I'm happy with the win of course,” Zvonareva said after being involved in the longest match in the history of the tournament, per the WTA's website.  

The 36-year-old came out on top in a deciding tie-break having been unable to hold on to an early 2-0 lead in the set.  

Anastasia Gasanova and Katarina Zavatska had set a new record for the longest contest earlier on Wednesday, the former eventually prevailing 6-2 6-7 (8-6), 7-5 after three hours and four minutes in an eventful first-round tie.

Ekaterina Alexandrova is another Russian player to progress to the last eight, seeing off Tereza Martincova in straight sets.

In the final match, Romanian qualifier Jaqueline Cristian surprised Jelena Ostapenko 6-3 7-6 (11-9) to reach her first ever WTA 500 quarter-final, where her opponent will be Kuznetsova.

Jelena Ostapenko wasted little time in her opening match at the St Petersburg Ladies Trophy, while there were also wins for Aliaksandra Sasnovich and Vera Zvonareva in Monday's action. 

Ostapenko needed less than an hour to get past Paula Badosa, who caused an upset when the pair met at last year's delayed French Open. 

There was to be no Roland Garros repeat for Badosa, though, as she was swept aside 6-2 6-2.  

The sixth-seeded Ostapenko started her campaign impressively in Russia, producing 26 winners and just eight unforced errors. Her serve was also in good order, never giving her opponent a chance of a break. 

Sasnovich had to work a little harder, rallying from a set down to see off Ana Bogdan 2-6 6-2 6-1. Her reward is a clash with third seed Fiona Ferro, who received a bye through to the second round.

Zvonareva, meanwhile, progressed in straight sets against Arina Rodionova, the Russian dropping just four games during a contest that lasted one hour and 22 minutes.  

Victory was sealed at the second opportunity, a sliced backhand into the net by her opponent sending Zvonareva through to the last 32.