World number one Novak Djokovic was full of praise for his Serbia Open semi-final conqueror Aslan Karatsev but bemoaned his own "low level" performance.

Karatsev got past Djokovic in the longest match of the 2021 ATP Tour in Belgrade, triumphing 7-5 4-6 6-4 on Saturday.

The match went for three hours and 25 minutes, with the Russian securing a spot in Sunday's final against 10th ranked Matteo Berrettini.

The Serbian had beaten Karatsev in the Australian Open semi-finals two months ago, with the 27-year-old Russian, who is now ranked 28th, returning the favour.

"From my side, I played on quite a low level, in my opinion," Djokovic said.

“[I had] some flashes of good quality tennis. I was fighting. That is a positive.

"I was really trying all the way [and] the crowd was great. They carried me and tried to lift me up, all the way to the end.

"Because of them, I think I won the second set. Unfortunately in the third, he was just the better player in the decisive moments. I had my chances, but that is sport."

Djokovic was gracious in defeat, offering a thumbs up immediately after Karatsev secured victory along with complimentary words to his opponent who saved 23 of 28 break points.

"Karatsev showed a lot of courage and that is why I gave him the thumbs up," Djokovic said.

"I felt like he deserved to win… Once the final point is done, there is never bad blood. We are rivals on the court, but I don’t hate anybody. I can’t be upset with him if he beat me.

"I have to be upset with myself and question why I lost the match. Whoever beats me deserves the credit and I gave him that.

"I lost to a better player who was just more courageous. He went for his shots at the right time and it worked for him."

Aslan Karatsev secured a stunning career-best victory over home favourite Novak Djokovic to set up a Serbia Open final against Matteo Berrettini.

Karatsev showed astonishing defiance to beat the world number one 7-5 4-6 6-4 in the longest ATP Tour match of the year on Saturday.

The third seed from Russia saved 23 of the 28 break points he faced as his aggressive approach paid off, toppling the 18-time grand slam champion in a contest that lasted three hours and 25 minutes.

It was sweet revenge for Karatsev, who was beaten by the legendary Serbian at the semi-final stage of the Australian Open two months ago.

Djokovic had won 11 matches in a row in his homeland, but bowed out despite being 2-0 up in the first two sets as a solitary break in the decider ended his run.

Karatsev, the world number 28, said: "It was a long, tough match [against a] tough opponent.

"You have to put [in] like 200 per cent to beat this guy, it's like playing against a wall. And he also made some good shots.

"He doesn't give you any free points. He always makes you play and you have to be always there because once you miss a couple of shots, he just takes it very quickly. That’s how I lost the second set."

Berrettini secured his place in the final with a 6-1 6-7 (5-7) 6-0 victory over lucky loser Taro Daniel.

Second seed Berrettini only lost six points in the last set after Daniel came from a break down in the second before winning a tie-break to take the second semi-final the distance.

Heading into Sunday's final, Karatsev and Berrettini have never previously faced each other on the ATP Tour.

Ash Barty will meet Aryna Sabalenka in the Stuttgart Open final after Simona Halep's quest to win the tournament for the first time fell short.

World number three Halep had claimed straight-set wins over Ekaterina Alexandrova and Marketa Vondrousova en route to the semi-finals, but met her match in the form of Belarusian Sabalenka, who triumphed 6-3 6-2.

A nine-time singles champion, Sabalenka made it into a 14th career final without conceding a single break, as she managed to keep Romanian Halep at arm's length.

Standing between Sabalenka and a 10th singles title is world number one Barty who, on her 25th birthday, came from behind to defeat Elina Svitolina 4-6 7-6 (7-5) 6-2.

Making her tournament debut in Stuttgart, Barty had overcome Laura Siegemund and Karolina Pliskova, but found herself at 5-4 down in the second set, with Svitolina serving for the match.

The fourth seed failed to take her chance, with Barty breaking and subsequently biting back in the tie-break, before carrying the momentum into the decider to claim a third straight win over Svitolina.

Top seed Elise Mertens made it to her second Istanbul Open as she saw off her doubles partner and birthday girl Veronika Kudermetova 6-1 6-4.

It means Mertens will be playing in two finals on Sunday, as she pairs up with Kudermetova again in the doubles showdown against Nao Hibino and Makoto Ninomiya.

Mertens' win ended Charleston champion Kudermetova's nine-match winning streak, and set up a final against the unseeded Sorana Cirstea, who defeated Marta Kostyuk 6-4 6-4.

Rafael Nadal.and Stefanos Tsitsipas will do battle for the Barcelona Open title on Sunday after both cruised into the final in straight sets.

Nadal beat fellow Spaniard Pablo Carreno Busta 6-3 6-2 to stand on the brink of being crowned champion for a 12th time at the Real Club de Tenis Barcelona 1899.

The top seed won 77 per cent of points on his first serve and returned superbly in yet another sublime clay-court exhibition.

Nadal broke Carreno Busta in his compatriot's first service game and ominously charged into a 5-1 lead in imperious fashion on Pista Rafael Nadal.

Carreno Busta broke back to prolong the opening set, but the 20-time grand slam champion wrapped it up in 45 minutes before swiftly taking charge of the second.

The world number three breezed into a 4-0 advantage and did not face a solitary break point as he took just shy of an hour and a half to set up a showdown with Tsitsipas, who knocked him out of the Australian Open at the quarter-final stage in February.

Tsitsipas maintained his magnificent form with a 6-3 6-3 defeat of Jannik Sinner.

The in-form Greek won the Monte Carlo Masters last weekend and matched Andrey Rublev's ATP tour-leading total of 26 victories this season by steering past Sinner.

Second seed Tsitsipas has won all 17 sets he has played on clay this season, having saved all four break points that Sinner earned.

World number one Ash Barty survived a scare to reach the semi-finals of the Stuttgart Open with a 2-6 6-1 7-5 win over Karolina Pliskova.

The Australian started slowly in the quarter-final of the WTA 500 tournament on Friday as Pliskova broke her serve twice in taking the first set, before Barty hit back with three breaks of her own to force a decider.

Barty was two points away from losing on five occasions as world number nine Pliskova served for the match at 5-4 in the final set.

But she broke the Czech's resolve eventually, sealing victory when Pliskova hit the ball long after a baseline rally.

The win was Barty's eighth consecutive victory over a top-10 opponent and she said in a media conference afterwards that facing top players in the world brings the best out of her.

"When you come up against top-10 opponents, you have to go to that level above to be able to compete. They force you to bring your best," Barty said.

"With a lot of the girls in the top 10, we've had plenty of matches that have gone either way, different experiences, so each time I love that challenge of testing myself against the best."

Barty will face Elina Svitolina in the semi-finals after she saved two match points to claim a 6-7 (4-7) 7-5 6-2 victory over Petra Kvitova.

In the other half of the draw, Simona Halep breezed through to the semi-finals with a 6-1 6-4 win over Ekaterina Alexandrova.

Halep clinically closed out the first set, and although Alexandrova showed more fight in the second, the world number three did not allow her a route back into the match.

Halep will face Aryna Sabalenka following the Belarusian's 7-5 4-6 6-1 win over Anett Kontaveit.

In the Istanbul Cup, top seed Elise Mertens secured her place in the semi-finals with a 6-4 6-4 win over Katerina Siniakova.

Mertens will face Veronika Kudermetova who fought back from a set down to clinch a 2-6 6-3 6-3 win over Ana Bogdan.

The other semi-final will see Sorana Cirstea play Marta Kostyuk. Cirstea progressed after Fiona Ferro, trailing 6-4, retired through injury while Kostyuk beat Ana Konjuh 7-5 4-6 6-3.

Simona Halep started her clay-court season in style at the Stuttgart Open as she saw off Marketa Vondrousova in straight sets on Thursday.

Second seed Halep is hunting her first appearance in a Stuttgart final, and she looked in fine form as she took just 56 minutes to dismiss Vondrousova 6-1 6-3.

Vondrousova – the 2019 French Open runner up – had won both of her previous meetings with Halep, but on this occasion she was no match for the world number three, who has won every major European clay-court tournament other than Stuttgart.

"Starting the clay-court season makes me very happy and motivated, extra motivated actually," Halep said in a post-match news conference.

"I missed playing matches. I had a few weeks without an official match and it was kind of tough when I started the match, but my mind was strong enough just to give focus on what I have to play. So, I did it great and today it was a great match.

"I was a little bit nervous before the match because I played twice against her and she beat me every time.

"It is important for my mind, for my game, because the clay-court season is going to be very tough. Now this match gave me confidence that my level is high, and if I keep doing the same thing, I will be good."

Facing Halep in the quarter-finals will be Ekaterina Alexandrova, who defeated world number 12 Belinda Bencic, and joining them in the final eight is Elina Svitolina, who defeated Angelique Kerber 7-6 (7-4) 6-3.

Two-time Stuttgart champion Kerber and Svitolina had faced off 13 times before Thursday's contest, and the Ukrainian is now 9-5 up in that head-to-head tussle.

While Aryna Sabalenka also progressed, Karolina Pliskova teed up a clash with top seed Ash Barty by coming from behind to beat Jelena Ostapenko 6-7 (7-9) 6-4 6-3.

At the Istanbul Open, top seed Elise Mertens also needed three sets to forge a path into the last night.

Mertens had to show her mettle in a contest which lasted over two hours, but she eventually got the better of Viktorija Golubic 6-4 4-6 6-1.

Veronika Kudermetova also made the last eight, as did Ana Bogdan, who fended off Barbora Kreijcova, while Fiona Ferro defeated Vera Zvonareva.

Rafael Nadal fended off Kei Nishikori to reach the quarter-finals of the Barcelona Open along with the in-form Stefanos Tsitsipas on Thursday.

Top seed Nadal secured an opening-set bagel in just 30 minutes, but Nishikori hit back to force a decider before the 20-time grand slam champion prevailed 6-0 2-6 6-2.

Nishikori hit only three winners as he was blown away in the first set, but broke twice in the second to ensure Nadal was taken to three sets in back-to-back matches for the first time in this tournament – having overcome Ilya Ivashka in the second round.

The world number three saved three break points from 0-40 down in the final set and Nishikori saw another two come and go, with a more clinical Nadal breaking twice to advance.

Nadal will now face unseeded Brit Cameron Norrie, who also won the first set 6-0 and was 5-3 down to David Goffin in the second when the Belgian retired due to a leg injury.

Newly-crowned Monte Carlo Masters champion Tsitsipas defeated Alex de Minaur 7-5 6-3, stretching his straight-sets winning streak to seven matches.

Next up for the second seed is a meeting with Felix Auger-Aliassime, who beat fellow Canadian Denis Shapovalov 6-2 6-3, while Jannik Sinner beat Roberto Bautista Agut 7-6 (11-9) 6-2.

Andrey Rublev, Diego Schwartzman and Pablo Carreno Busta also made it through.

Two seeds fell in the Serbia Open, with Federico Delbonis taking out Dusan Lajovic 6-3 2-6 6-4 and Taro Daniel defeating John Millman 3-6 6-2 6-3.

Gianluca Mager moved into the quarter-finals at the expense of Alexei Popyrin and Aslan Karatsev battled past Aljaz Bedene 6-3 4-6 7-6 (7-5) in Belgrade.

Carla Suarez Navarro revealed on Thursday she has overcome Hodgkin lymphoma, and the Spaniard is set to resume her tennis career.

The former world number six revealed last September she would undergo six months of chemotherapy after being diagnosed with the rare cancer.

Suarez Navarro vowed at the time to show "positivity in the face of adversity" and the 32-year-old has now announced she is cured.

The 32-year-old posted on social media: "Another step forward. Today I finished my treatment and overcame Hodgkin lymphoma.

"Thanks to all for your warm messages. Every word of support gave me strength during the past few months.

"All my gratitude to healthcare professionals who take care of us every day. I'M CURED!"

Carla Suarez Navarro announced two years ago that the 2020 season would be her last on the WTA Tour.

However, the WTA said she decided to has abandon that plan and would return to action, confirming her entry for the French Open which begins on May 30 in Paris.

Novak Djokovic thought he was "pretty flawless" in his first match of the Serbia Open, but Rafael Nadal was given a scare in his clash with qualifier Ilya Ivashka at the Barcelona Open.

World number one Djokovic suffered a shock third-round exit to Dan Evans at the Monte Carlo Masters last week but ruthlessly dispatched Kwon Soon-woo 6-1 6-3 in his home city of Belgrade.

Djokovic broke his opponent five times to set up a meeting with eighth seed and fellow Serbian Miomir Kecmanovic, who battled past qualifier Arthur Rinderknech in three sets, in the quarter-finals.

"I thought it was a pretty flawless performance," Djokovic said. "I moved well, I was mixing up the pace quite well, making him play. I served well in the important moments, [and] overall I just felt great."

On playing in front of his family and friends, the two-time Serbia Open champion added: "It gives you an extra push, an extra motivation, energy to really give your best and leave it all out on the court.

"I think also that made me feel comfortable and confident on the court and I played really good. I'm really pleased with the quality of tennis."

Second seed Matteo Berrettini defeated fellow Italian Marco Cecchinato 6-4 6-3 and will face either Filip Krajinovic or Nikola Milojevic in the last eight of the clay-court tournament.

Over in Barcelona, Nadal – an 11-time champion at the event – was out to make a statement after a rare defeat on the dirt to Andrey Rublev in Monte Carlo.

But the 'King of Clay' needed two hours and 20 minutes to fight back against the unheralded Ivashka 3-6 6-2 6-4 to reach the round of 16, where he will face Kei Nishikori. Nadal is now 62-4 at a tournament where he once won 41 straight matches.

Second seed and Monte Carlo champion Stefanos Tsitsipas hammered Jaume Munar 6-0 6-2, while third seed Rublev - runner-up to the Greek on Sunday - joined Pablo Carreno Busta (6) and Alex De Minaur (14) in making it through.

Evans was unable to follow up his run in Monte Carlo with the 16th seed beaten by Corentin Moutet in a lengthy three-setter, while Fabio Fognini (9) was defaulted for unsportsmanlike conduct after verbally abusing a line official when trailing 6-4 4-4 to Spanish qualifier Bernabe Zapata Miralles.

Athletes expressed relief and vowed to continue the fight for reforms after a jury in Minnesota found a former police officer guilty in the May 2020 death of George Floyd. 

Derek Chauvin was convicted of second-degree murder, third-degree murder and second-degree manslaughter on Tuesday, nearly 11 months after he knelt on Floyd's neck and back for more than nine minutes during an arrest. 

Floyd's death aged 46 sparked outrage across the United States, with athletes across multiple sports among those who called for justice. 

Tuesday's verdict in Minneapolis provided a measure of progress and sports figures, teams and leagues spoke out after the ruling. 

Basketball star LeBron James' reaction was among the most succinct as he tweeted simply: "ACCOUNTABILITY".

Boxing legend Mike Tyson tweeted: "Guilty. Justice served."

While similiar expressions of relief were common, most continued to lament the crime that sparked the case. 

"George Floyd lost his life, as many others have, unjustly. We can't forget that - that people are losing their lives," Brooklyn Nets head coach Steve Nash told reporters.

"On the other hand, it is a small gesture of justice and possibly hope for the future in that perhaps all the social justice movements - the NBA, the WNBA, the community at large - are really making an impact.

"I just hope that this is the type of statement by our justice system that gives hope and precedence for these type of verdicts to be the norm."

Jannik Sinner set up a clash with Roberto Bautista Agut at the Barcelona Open as he vowed to keep making progress after cracking the top 20 for the first time.

Italian 19-year-old Sinner is a fast-rising new star of the men's game and now has a ranking to match his age. However, he was put in his place by Novak Djokovic last week in Monte Carlo, before the world number one was himself dealt a jolting defeat by Dan Evans.

Sinner sped past Belarusian Egor Gerasimov in the first round in Barcelona on Tuesday, winning 6-3 6-2, and it will be wily world number 11 Bautista Agut who stands in his way of going deeper into the tournament.

In two meetings on hard courts this season, Sinner has edged out 33-year-old Spaniard Bautista Agut in tight deciding sets, and now they face a reunion on clay.

"He lost in Dubai against me, he lost in Miami against me, now we play once more here, so it's quite a small period of time," said Sinner.

"We're playing now our third match already, so it's going to be a very tough match. He is very, very solid. I never played against him on clay. I'm trying to be ready in the best possible way."

Bautista Agut barged past fellow Spanish player Pablo Andujar, scoring a 6-4 6-0 win.

Sinner was proud to enter the ATP top 20 this week but sees it as just a step on his journey, saying: "Obviously it's a good number, but for me at the moment not that important."

He added, quoted on the ATP website: "[I'm] just trying to improve day after day with my team and trying to improve as a player and the ranking is what it is. I'm happy to be top 20 player but the road is long so a lot of work to do."

Albert Ramos-Vinolas, Lorenzo Musetti and Frances Tiafoe, who fought off 17-year-old Spanish prospect Carlos Alcaraz, were also among Tuesday's winners in Barcelona.

Star turn Djokovic begins his campaign at the Serbia Open on Wednesday when he tackles Kwon Soon-woo, with the 18-time grand slam winner having received a first-round bye.

Tuesday's play in Belgrade saw wins for, among others, Federico Delbonis, Aljaz Bedene and Miomir Kecmanovic.

Petra Kvitova brushed aside Jennifer Brady as the defending champion cleared her first hurdle at the Stuttgart Open.

The Czech left-hander was the last winner of the German tournament, beating Anett Kontaveit in the 2019 final, with last year's event cancelled due to the pandemic.

Kvitova was handed a tough opening assignment against Australian Open runner-up Brady, but the American's streak of defeats since that Melbourne final defeat extended to three as Brady lost 6-4 6-3 in an hour and 32 minutes.

Two-time former Wimbledon champion Kvitova, seeded seventh, picked apart the Brady serve once in each set and fended off three break points across the contest to secure her last-16 place.

She was joined in the second round by powerful Belarusian Aryna Sabalenka, as the fifth seed scorched to a 6-2 6-2 win over China's Zhang Shuai.

Earlier, Ekaterina Alexandrova, Kontaveit, Anna Lena Friedsam and Laura Siegemund also went through to the last 16 of the WTA 500 event.

Meanwhile, Fiona Ferro caused a shock at the Istanbul Cup as she landed a 7-5 6-2 first-round win over former champion Petra Martic.

Martic, seeded second this year and ranked 21st in the world, landed the title in Istanbul in 2019 but was rolled over by French player Ferro in an hour and 45 minutes, in a match featuring seven breaks of serve.

Veronika Kudermetova followed her recent maiden title in Charleston with a nerve-jangling first-round win against Bernarda Pera, the fifth seed scrambling through 6-4 3-6 7-6 (7-4).

There was no such toil for top seed Elise Mertens, a 6-2 6-0 winner against Lara Arruabarrena, or for Daria Kasatkina, who dished out a 6-1 6-0 drubbing to Tereza Mrdeza.

Kasatkina is seeking her third title of 2021, having won previously in Melbourne and St Petersburg.

Anastasia Pavlyuchenkova bowed out of the WTA 250 event though, beaten 7-6 (7-2) 6-7 (8-10) 6-4 by compatriot Anastasia Potapova.

Kei Nishikori's comeback surprised the former world number four, who survived a major scare to advance at the Barcelona Open.

Nishikori trailed 6-4 4-2 and was forced to break serve as Guido Pella attempted to close out the match in the second set, before sensationally rallying to a 4-6 7-6 (7-4) 6-2 win on Monday.

A two-time champion at the ATP 500 tournament on the Barcelona clay, Nishikori broke serve on three occasions in the final set en route to the second round.

"He had the match today at 6-5, serving [for the match]," said Nishikori. "He was much better in the first and second [sets] and 3-0 up in the tie-break. I don't know how I fought through. [In the] third set, I was playing much better.

"I was making so many unforced errors in the first and second [sets]. Maybe he got a little bit tired and I was playing strong in the third set. I want to take that to the next round… The way I fought today and the way I played in the third set was good."

Next up for 2014 US Open finalist Nishikori is 13th seed Cristian Garin.

Ilya Ivashka topped Tallon Griekspoor 6-3 6-1 and the qualifier's reward is a showdown with top seed and 20-time grand slam champion Rafael Nadal.

Cameron Norrie, Pablo Andujar, Jeremy Chardy, Pierre-Hugues Herbert, Jaume Munar, Federico Gaio, Egor Gerasimov and Bernabe Zapata Miralles all advanced to the last 32.

At the Serbia Open, seeds Filip Krajinovic and John Millman booked their spots in the round of 16.

With the ATP 250 tournament being staged for the first time since 2012 and headlined by world number one Novak Djokovic, Serbian fifth seed Krajinovic overcame Stefano Travaglia 7-5 5-7 6-3 in a Belgrade rollercoaster.

Millman – the Australian seventh seed – took down local wildcard Danilo Petrovic 7-5 6-4 as Marco Cecchinato and Nikola Milojevic won through.

Belinda Bencic claimed her first win on clay since the 2019 French Open as she saw off teenager Nastasja Schunk at the Stuttgart Open.

The world number 12 eased to a 6-4 6-2 victory over the 17-year-old qualifier, who saved five match points in her final service game before Bencic closed things out.

"My love affair with clay is... I'm trying to improve myself on it," Bencic said after her first-round triumph.

"I think I'm getting better and I'm taking falls sometimes. I'm trying my best on this surface."

Maria Sakkari was similarly comfortable in progressing to the next round, hitting 24 winners as she dispatched Andrea Petkovic 6-2 6-2 on her debut at the tournament.

At the Istanbul Cup, four of the five scheduled matches were completed before rain stopped play with Anastasia Pavlyuchenkova and Anastasia Potapova level at a set apiece.

Eighth seed Wang Qiang fought back from a set down to beat Anastasia Gasanova 4-6 6-1 6-2.

There were also wins for Ana Konjuh, Katerina Siniakova and Viktorija Golubic.

Australian Astra Sharma scored a shock win over top seed Ons Jabeur in the final of the MUSC Health Women's Open, landing her first WTA Tour singles title.

The world number 165 made a slow start to the match but eventually overwhelmed Jabeur 2-6 7-5 6-1 in Charleston.

Having risen to 27th in the world rankings without a trophy to her name, the 26-year-old Jabeur looked to have an ideal opportunity to put that right.

Sharma recovered from the one-sided opening set to lead early in the second, and despite Jabeur getting it back on serve, the underdog surged ahead again to level the contest.

In her second WTA singles final and first for two years, Sharma went one step further than when she was runner-up in Bogota, racing through the deciding set as she swatted away Jabeur's threat.

Jabeur said the defeat was "very tough" to take, while Sharma said of her breakthrough week: "This has been an amazing event. I've really enjoyed playing here."