Daria Kasatkina claimed the fourth title of her career after Margarita Gasparyan retired in the second set of the St Petersburg Ladies Trophy final with a back injury.

Kasatkina, who becomes the first player to win two WTA tournaments in 2021 having claimed the Phillip Island Trophy last month, was leading 6-3 2-1 when Gasparyan pulled out.

Gasparyan initially took a medical timeout after losing her first two service games of the match to trail 4-1 before eventually retiring after dropping her serve early in the second set.

Kasatkina's triumph meant she became the first player to win both WTA 500 events on Russian soil, previously claiming the 2018 Moscow title at this level.

The former top-10 player has endured a dip in recent seasons but will be back in the top 50 on Monday, while wildcard Gasparyan's maiden WTA 500 final means she returns to the top 100.

Kasatkina dropped the opening set in her quarter-final and semi-final matches but then swept through the next two sets emphatically on each occasion.

"I'm proud of how I was able to manage the pressure," Kasatkina said, quoted on the WTA website. "I felt differently during this tournament and I'm really proud of that."

German star Alexander Zverev was too strong for top seed Stefanos Tsitsipas in the Mexican Open final, claiming the title in straight sets after a stunning turnaround.

In a battle of the top two seeds, Zverev reigned supreme 6-4 7-6 (7-3) for his 14th ATP crown in Saturday's Acapulco decider.

Last year's US Open finalist Zverev was runner-up at the ATP 500 tournament in 2019, beaten by Australian Nick Kyrgios in straight sets.

But Zverev went one step further this year, taking down two-time Australian Open semi-finalist Tsitsipas after two hours, 17 minutes.

Zverev, who was rocked during his semi-final win over countryman Dominik Koepfer on Friday – a 5.7 magnitude earthquake registered as broadcast cameras shook, did not drop a set throughout his title-winning run.

Greek star Tsitsipas made an impressive start, racing out to a 3-0 lead after breaking Zverev in the second game.

Zverev, though, hit back as he put the set back on serve in the seventh game before consolidating.

Another break saw Tsitsipas come unstuck – Zverev reeling off six consecutive games to claim the opening set in red-hot fashion.

Zverev and Tsitsipas went toe-to-toe in the second set, the pair exchanging breaks late as a tie-break eventually saw the former complete a dominant display.

Leylah Fernandez and Viktorija Golubic will go head-to-head in the Monterrey Open after progressing on Saturday.

Canadian teenager Fernandez reached her second career WTA Tour singles final thanks to a 7-5 7-5 win over seventh seed Sara Sorribes Tormo.

The 18-year-old Fernandez – whose first final came via last year's Mexican Open in Acapulco, where she lost – converted six of nine break points and hit 35 winners.

Standing in Fernandez's way is Switzerland player Golubic.

Golubic upstaged eighth seed Ann Li 6-2 6-4 to become the first qualifier to advance to the Monterrey Open final in the tournament's history.

The 28-year-old Golubic also reached the Lyon Open final two weeks ago – beaten by Clara Tauson.

Aslan Karatsev captured the first ATP Tour title of his career as the late-blossoming Russian triumphed in the final of the Dubai Tennis Championships.

At the age of 27, and with little warning, Karatsev has hurtled from obscurity before tennis went into lockdown 12 months ago to real prominence.

A 6-3 6-2 victory over South African Lloyd Harris on Saturday gave him a trophy for his efforts and he will enter the top 30 on Monday, having never had a double-digit ranking before this season.

Karatsev reached the Australian Open semi-finals last month, having had to win three qualifying rounds to make the main draw, and it took Novak Djokovic to stop that charge in Melbourne.

Now Vladikavkaz-born Karatsev is back in another winning routine, with Andrey Rublev, Jannik Sinner and Dan Evans having figured among his victims en route to the Dubai final.

The first-time champion said on Amazon Prime: "I am super happy. It was a tight match. [I was] really nervous. I want to congratulate my opponent for the final [run]. He did a great week. Every final is different, so I am happy that I won."

Karatsev had some promising results at Challenger Tour level last year but had never shown form on the main circuit until the start of 2021, and suddenly he looks a major force to be reckoned with.

He said of the rush of success: "You never know when it is coming. I did a good job with my team, with my coach and it has happened now."

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.

Tokyo 2020 organisers have announced spectators will not be allowed to travel from overseas to watch the Olympic Games this year.

The measure has been taken as part of an effort to reduce the risks of COVID-19 spreading at the delayed Games.

The Games will run from July 23 to August 8, having been set back by a year due to the global health crisis.

Also affected will be the Paralympics, which runs from August 24 to September 5, with travelling spectators also barred from attending.

The International Olympic Committee (IOC) and International Paralympic Committee (IPC) have been advised of Tokyo's decision and are said by Games chiefs to "respect and accept this conclusion".

In a statement issued on Twitter, Tokyo 2020 said: "Today, on March 20, we reported to the IOC and IPC that we would not accept overseas spectators to Japan in order to realise a safe and secure event.

"We will continue to do our utmost to make this summer's event a safe and secure event so that it will be a light of hope for people all over the world."

In a further statement, Tokyo 2020 organisers said tickets purchased by those planning to travel from abroad would be refunded.

They said the coronavirus situation within and beyond Japan "remains very challenging" and pointed to travel across borders being "severely restricted", meaning entry to Japan could not be guaranteed.

"In order to give clarity to ticket holders living overseas and to enable them to adjust their travel plans at this stage, the parties on the Japanese side have come to the conclusion that they will not be able to enter into Japan at the time of the Olympic and Paralympic Games," said the Tokyo 2020 statement.

"This conclusion will further contribute to ensure safe and secure Games for all participants and the Japanese public."

World number five Stefanos Tsitsipas cruised into the Mexican Open final with a routine victory over Italian teenage sensation Lorenzo Musetti in Acapulco on Friday.

Tsitsipas triumphed 6-1 6-3 in 79 minutes to get past 19-year-old Musetti, who had beaten third seed Diego Schwartzman and former world number three Grigor Dimitrov on his run to the semis.

The Greek top seed will play second seed Alexander Zverev in Saturday's final after the German got past countryman Dominik Koepfer 6-4 7-6 (7-5) in their semi-final, which was literally rocked by an earthquake.

The broadcast cameras shook mid-point but play continued as a 5.7 magnitude earthquake was registered to the north of Marquelia, which is to the east of Acapulco.

Tsitsipas holds a 5-1 record against Zverev, who is ranked seventh in the world and made last year's US Open final.

"Sascha is someone I've played against in the past and it's never easy. We're both really hungry and we're both very competitive," Tsitsipas said.

The Greek made light work of Musetti, winning five straight games in the opening set after starting at 1-1.

Unforced errors cost Musetti, who had his moments, but Tsitsipas was on song with 17 of 23 winners off his forehand.

Musetti will move into the top 100 of the rankings for the first time on Monday after his breakthrough week.

"We'll definitely see a lot from Lorenzo in the future, he has a wonderful one-handed backhand and creates lots of opportunities. He showed his level this week," Tsitsipas said.

Eighth seed Ann Li toppled the top remaining seed Zheng Saisai in the quarter-finals of the Monterrey Open on Friday, throwing the field wide open.

Li triumphed 7-5 6-1 over third seed Zheng, who held the highest rank of all remaining players after Sloane Stephens and Nadia Podoroska's first-round exits.

World number 52 Zheng struggled to win on her first serve, with Li converted five of seven break points.

American Li, who is ranked 72nd in the world, will next face Swiss qualifier Viktorija Golubic, who beat Russia's Anna Kalinskaya 6-2 6-4.

On the other side of the draw, Canadian Leylah Fernandez defeated Slovakia's Viktoria Kuzmova 7-5 6-3 and will face seventh seed Sara Sorribes Tormo in the other semi-final.

Sorribes Tormo, who is now the highest ranked remaining player, defeated Anna Karolina Schmiedlova 6-3 7-5.

An earthquake hit Acapulco during Alexander Zverev's clash against Dominik Koepfer at the Mexican Open on Friday.

The broadcast camera shook mid-point during the all-German semi-final encounter.

A 5.7 magnitude earthquake was registered to the north of Marquelia, which is to the east of Acapulco.

Zverev went on to secure a 6-4 7-6 (7-5) victory over Koepfer to reach the final.

World number one Novak Djokovic has joined Rafael Nadal and Roger Federer in deciding not to play at the Miami Open, which begins next week.

The Masters 1000 tournament has not been its usual big draw for the leading men this year, and Djokovic becomes the latest high-profile withdrawal.

The 33-year-old Serbian announced he would enjoy some family time rather than travel to the United States, citing the need for balance in his life as coronavirus restrictions affect globe-trotting sports stars.

Miami's total prize fund is said to have been cut from $16.7million in 2019, the last time it was held, to $6.68m this year.

That drastic reduction, reported by the Tennis Majors website, may or may not have been a partial factor in the withdrawals that have dented the top-tier quality in the men's side of the tournament.

The women's event looks like being a full-strength field, while new world number two Daniil Medvedev is set to be the men's top seed, providing he makes the trip.

Djokovic wrote on Twitter: "Dear fans, I'm very sorry to announce that this year I won't travel to Miami to compete.

"I decided to use this precious time at home to stay with my family. With all restrictions, I need to find balance in my time on tour and at home. I look forward to coming back next year!"

Nadal has been bothered by a back problem and cited it earlier this week as the reason for his withdrawal, as he looks to recover full fitness in time for the clay-court season and a crack at winning a 14th French Open title.

The Spaniard's great rival Federer, a fellow 20-time grand slam winner, has only just returned from a year away from the tour after knee surgery, and beat Dan Evans in his first match back at the Qatar Open before losing to Nikoloz Basilashvili.

Federer then elected not to play in Dubai and will not be in Miami, where he is the men's reigning champion, having taken the 2019 title. The 2020 tournament was cancelled because of the COVID-19 crisis.

Andrey Rublev's ATP 500 winning streak came to an end at the hands of Aslan Karatsev on a history-making day at the Dubai Tennis Championships.

Rublev had won 23 consecutive matches at this level, second only to Roger Federer (28), but Karatsev finally ended the Russian's remarkable run to progress to his first ATP singles final.

Karatsev, who incredibly went from qualifying to the semi-finals of the Australian Open this year, defeated his compatriot 6-2 4-6 6-4.

He became the first Wild Card to reach the final since Thomas Muster in 1997, doing so by hitting 41 winners and forcing 16 break points – of which he won four – during two hours and 12 minutes on court.

"It was a really tight match [against a] tough opponent," Karatsev said in his on-court interview.

"It was an unbelievable performance [from Andrey]. He didn't lose a match at an ATP 500 in [one year]. Everything was decided in one or two points, I feel happy."

The championship match will be between two first-time Dubai finalists after Lloyd Harris stunned Denis Shapovalov in the other semi-final.

World number 81 Harris, who overcame top seed Dominic Thiem, 14th seed Filip Krajinovic and former US Open finalist Kei Nishikori to reach the last four, came from a set and 4-2 down to defeat world number 12 Shapovalov.

He prevailed 6-7 (5-7) 6-4 7-6 (8-6) to reach a maiden ATP 500 final and become the first qualifier to reach the showpiece in Dubai.

"I don't have many words right now. I am super happy with that win," Harris said on court afterwards.

"Being a set and 2-4 down is mentally and physically a little bit troublesome for me, but I found my best tennis from there. I am just extremely happy with the result right now."

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."

Top seed Stefanos Tsitsipas was made to sweat but got past Felix Auger-Aliassime in three sets to reach the Mexican Open semi-finals on Thursday.

World number five Tsitsipas, who was a semi-finalist at last month's Australian Open, defeated seventh seed Auger-Aliassime 7-5 4-6 6-3 in Acapulco.

In a tight contest, back-to-back double faults from Canadian sensation Auger-Aliassime in the eighth game of the third set proved costly as Tsitsipas broke after the pair had held serve throughout the last.

"It got really tight," Tsitsipas said in his post-game interview. "I got a bit lucky with the double faults towards the end of the match.

"I was just persistent. Towards the end I had zoned in 100 per cent. Both of us brought an amazing energy out on the court. Felix is someone I've played a lot and I have huge respect for him."

Greek star Tsitsipas will next play emerging Italian teenager Lorenzo Musetti for a spot in the ATP 500 tournament decider.

Qualifier Musetti, who upstaged third seed Diego Schwartzman in the first round, stunned fifth seed Grigor Dimitrov 6-4 7-6 (7-3) in the final match of the day.

The 19-year-old Musetti will now contest his maiden ATP 500-level semi-final as he prepares to enter the top 100 on the men's tour after just his fourth main-draw appearance.

Alexander Zverev – the German second seed – progressed to the semi-finals with a walkover after eighth seed Casper Ruud withdrew due to a wrist injury sustained in practice.

Zverev will play countryman Dominik Koepfer in the final four after he defeated Cameron Norrie 7-5 6-4, maintaining his run of not dropping a set all tournament.

Third seed Zheng Saisai comfortably accounted for countrywoman Zhu Lin to reach the quarter-finals of the Monterrey Open on Thursday.

Zheng, who is ranked 27th in the world, triumphed 6-1 6-2 in a dominant display where she was seldom challenged.

In the last eight, Zheng will face eighth seed Ann Li, who overcame Slovenian Tamara Zidansek 6-4 6-3 at the WTA International tournament.

Zheng is the highest remaining seed left standing in the draw after the first-round exits of top seed Sloane Stephens and Nadia Podoroska.

Russian qualifier Anna Kalinskaya continued her good run with a 6-4 6-3 victory over Nina Stojanovic and she will next face Viktorija Golubic in the quarters – the latter topped Lauren Davis 6-3 6-1.

A record seven Russians will contest the quarter-finals of the St Petersburg Ladies Trophy after victories for seeds Veronika Kudermetova and Daria Kasatkina on Thursday.

Number two seed Kudermetova edged past Kamilla Rakhimova 7-5 3-6 7-6 (7-5), while eighth seed Kasatkina also needed three sets to see off Aliaksandra Sasnovich 5-7 6-3 7-6 (7-2). 

Wildcard Margarita Gasparyan held off Katerina Siniakova 6-4 6-4 and qualifier Anastasia Gasanova shocked fifth seed Anastasia Pavlyuchenkova 1-6 7-6 (10-8) 7-6 (7-4). 

They joined fellow Russians Vera Zvonareva, Ekaterina Alexandrova and Svetlana Kuznetsova in the last eight, with Romanian qualifier Jaqueline Cristian also in the line-up.

The previous highest number of Russians in a WTA quarter-final line-up was six, set at Moscow 2005 when Kuznetsova was joined by Dinara Safina, Elena Dementieva, Maria Sharapova, Anastasia Myskina and Elena Likhovtseva.

The last time a single nation had as many players at this stage of a WTA event was in Oakland in 1993 when the United States produced seven of the eight quarter-finalists.