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.

Denis Shapovalov secured a straight-sets win over Jeremy Chardy to set up a semi-final showdown with qualifier Lloyd Harris at the Dubai Tennis Championships. 

The third seed struck 26 winners en route to a 7-5 6-4 triumph on Thursday, but it was his serve that pleased him most.

Shapovalov, ranked 12th in the world, sent down 10 aces as Frenchman Chardy was deprived of any break-point openings.

"I've focused on my serve a lot in the past couple of weeks," the Canadian said.

"I have worked on placing it and tried out different types of serves to have more variation. I hope I can continue that.

"I've also worked on my footwork and positioning during rallies. I am feeling the ball well on both sides. If I am moving well, everything goes into place."

Harris was a surprise winner over Kei Nishikori, sealing a 6-1 3-6 6-3 success to dump out the former world number four.

Second seed Andrey Rublev defeated Marton Fucsovics 7-5 6-2 and will now face fellow Russian Aslan Karatsev.

Wildcard Karatsev continued his run with a hard-fought victory over teenager Jannik Sinner, coming from a set down in a 6-7 (5-7) 6-3 6-2 win.

Top seed Stefanos Tsitsipas and fellow star Alexander Zverev progressed to the Mexican Open quarter-finals on Wednesday, but Milos Raonic bowed out.

Tsitsipas was too good for big-serving American John Isner in a 6-3 6-2 victory in Acapulco midweek.

A two-time Australian Open finalist, having also reached the French Open final four last year, Tsitsipas excelled on serve against Isner.

Greek star Tsitsipas only dropped one point on his first serve – not facing a break point throughout the last-16 contest – while firing down eight aces.

Standing in the way of Tsitsipas and a semi-final spot at the ATP 500 tournament is Canadian sensation Felix Auger-Aliassime.

In a battle of the NextGen, seventh seed Auger-Aliassime saved four of five break points in a 6-3 6-4 win over wild card Sebastian Korda.

Zverev will feature in his third Mexican Open quarter-final in four years after the second seed took down Laslo Djere 6-4 6-3.

Runner-up in 2019, Zverev will next face eighth seed Casper Ruud – who topped Tallon Griekspoor 4-6 6-3 7-6 (7-3) in the quarters.

"I think today what showed the most is that I got better with the match," Zverev said. "I started off extremely sloppy, started off with a lot of unforced errors.

"The longer the match went on the better I started playing and this is something that is very important for me. When I get into a rhythm I feel very comfortable on court and that's how I felt today."

Elsewhere, Lorenzo Musetti's giant-slaying run continued following a 2-6 6-3 7-6 (7-1) victory against Frances Tiafoe.

Musetti earned his first ATP 500 quarter-final as the Italian prepares to meet fifth seed Grigor Dimitrov, who eased past Miomir Kecmanovic 6-4 6-2.

There was an upset after fourth seed Raonic crashed out 6-4 6-2 at the hands of Dominik Koepfer, while sixth seed Fabio Fognini lost 6-4 6-3 against Cameron Norrie.

Canadian teenager Leylah Fernandez booked her spot in the Monterrey Open quarter-finals after easing past Kristina Kucova.

Fernandez cruised into the last eight of the WTA International tournament on Wednesday by defeating Slovakia's Kucova 6-1 6-4 in Mexico.

Kucova had eliminated top seed and 2017 US Open champion Sloane Stephens on Tuesday, but she was no match for the 18-year-old Fernandez midweek.

Next up for Fernandez is Viktoria Kuzmova, who beat lucky loser Harriet Dart 6-4 6-3.

Spanish seventh seed Sara Sorribes Tormo did not have to take to the court, benefiting from a walkover after Kaja Juvan withdrew.

Sorribes Tormo will face Anna Karolina Schmiedlova, who outlasted Jasmine Paolini 2-6 6-2 6-2.

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.

Jannik Sinner fought hard to earn an impressive victory that knocked fourth seed Roberto Bautista Agut out of the Dubai Tennis Championships. 

The 19-year-old rising star, who won the Great Ocean Road Open last month, prevailed in a match that remained in the balance until the end on Wednesday. 

Sinner won 6-4 3-6 7-5 to reach the quarter-finals, with Bautista Agut following top seed Dominic Thiem - who lost in the second round - out of the tournament. 

After hitting 16 aces, Sinner – the youngest player in the ATP Tour top 100 – will face surprise Australian Open semi-finalist Aslan Karatsev next. 

Second seed Andrey Rublev is through after a comfortable 6-3 6-1 win over Taylor Fritz. 

Rublev will face Marton Fucsovics, who ousted Serbian Dusan Lajovic in three sets, in the last eight. 

The Russian now has 22 consecutive wins at ATP 500 events, a run that has included four titles at that level. Only Roger Federer has ever recorded a longer streak, doing so with a run of 28 between 2014 and 2016.

"I am really happy that I can win in straight sets and quite confidently," Rublev said. 

"I know Taylor since [the] juniors and it is always tough to play against him, because he has a huge serve and he is playing really fast. 

"The first set was not even rallies because everything was serve, winner or serve, mistake, so everything was so fast. 

"In these conditions, it is tough to find the rhythm. You don't know what's going to happen and it's really not easy, but I'm happy that in the end I made it."

Third seed Denis Shapovalov is also through after a 6-4 6-3 win over Hubert Hurkacz, the Canadian booking a last-eight meeting with Jeremy Chardy. 

Kei Nishikori will play Lloyd Harris in the other quarter-final. 

Italian qualifier Lorenzo Musetti may be ranked 120th in the world but he claimed his maiden top-10 scalp on Tuesday, beating Diego Schwartzman in the first round of the Mexican Open.

Musetti, the Australian Open boys' singles champion in 2019, secured a 6-3 2-6 6-4 win over ninth-ranked Schwartzman in a stunning success.

"There is a lot of work, a lot of sacrifice and I think some tears left in my eyes," the 19-year-old said during his on-court interview.

"I'm really proud of myself, but now I'm going to work harder and focus on the next days."

Musetti, whose forehand was excellent, defeated both Stan Wawrinka and Kei Nishikori at the Internazionali d'Italia in Rome last year.

Top seed Stefanos Tsitsipas had no such trouble, easing into the second round, where he will face big-serving American John Isner.

The Greek world number five beat France's Benoit Paire 6-3 6-1, aided by a strong display on serve.

"I didn't know what to expect from Benoit today," Tsitsipas said. "I think it's kind of tricky playing a tournament you haven't played before."

On facing 27th-ranked Isner next up, Tsitsipas added: "He's a guy that serves really well so that's going to be the biggest element and the one thing that I'll really have to resolve during that match."

Fourth seed Milos Raonic sent down 13 aces as he defeated American Tommy Paul 7-6 (8-6) 6-4.

In the late match, fifth seed Grigor Dimitrov got past Adrian Mannarino, who retired when trailing 6-4 3-0.

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).

Top seed Dominic Thiem was beaten in straight sets in the second round of the Dubai Tennis Championships by Lloyd Harris.

The reigning US Open champion, given a bye for the first round, lost 6-3 6-4 to his South African opponent, who sits 77 places further down the ATP rankings.

The Austrian has endured a difficult start to 2021. He lost in straight sets to Grigor Dimitrov in the last 16 of the Australian Open and was beaten by Roberto Bautista Agut in the quarter-finals in Doha.

It was a first win over a top-five player for Harris, who was not once taken to deuce on serve during their 72 minutes on court.

"I'm super, super happy with that win. [He is] by far the highest-ranked player I have beat," said Harris. "I look up to Domi a lot so, for me, it is a special feeling. I am really happy. Just the fact that I am playing good tennis, match in, match out now is giving me a lot of confidence.

"I was serving really well. I don't think I faced any break points. I took control of those games and [in] one or two games on his serve, I gave myself a good look. I played some of the important points very well. I am very proud of that."

While Thiem is struggling for form, things are looking far better for Andrey Rublev, who beat Emil Ruusuvuori 6-4 6-4 to stretch his winning streak at ATP 500 events to 21 matches.

The world number eight, who will face Taylor Fritz in the next round, equalled Andy Murray for the second-best winning run at this level of the Tour. Roger Federer (28) holds the record.

Third seed Denis Shapovalov beat Jan-Lennard Struff for the loss of just four games, while Bautista-Agut advanced after opponent Matthew Ebden retired in the first set.

Fifth seed David Goffin was beaten in straight sets by Kei Nishikori, who recorded just his third victory of the year.

Karen Khachanov and Jannik Sinner each advanced after three-setters, while Marton Fucsovics and Aslan Karatsev were also taken the distance before progressing.

Hubert Hurkacz, Lorenzo Sonego, Dusan Lajovic, Aljaz Bedene and Filip Krajinovic also won on Tuesday.

Daria Kasatkina fended off fast-rising star Clara Tauson at the St Petersburg Ladies Trophy as the Russian home favourite edged a clash of recent tournament winners.

Former world number 10 Kasatkina, who landed the Phillip Island Trophy title in Melbourne last month, came through a roller coaster second set against the qualifier to tie up a 6-4 7-6 (7-0) first-round victory.

Former junior world number one Tauson won the Lyon Open at the start of March, and the 18-year-old Danish player twice broke when Kasatkina was serving for the match to take their tussle to a tie-break that was then unexpectedly one-sided.

Having been jittery when serving at 5-4 and 6-5, Kasatkina found composure when it mattered to see out the match.

Tauson had won 13 consecutive matches, including qualifiers, and had reeled off 20 successive sets during that run, but Kasatkina interrupted the hot streak.

Three-time WTA tournament winner Kasatkina, seeded eighth this week, said on Amazon Prime: "You're right, I was nervous serving for the match, but I'm glad I could close out the match playing the tie-breaker.

"Sure, there is something to improve, but I don't want to talk about it right now. I'm going to talk to my coach about what I need to improve. She wasn't an easy opponent. She just won a tournament and I knew it was going to be a tough match, and a tough match it was."

Two 19-year-old qualifiers were also among Tuesday's winners, as Chinese player Wang Xinyu and Russian Kamilla Rakhimova safely went through to the last-16 stage.

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