Barbora Krejcikova saved seven match points on her way to beating Anett Kontaveit in a thrilling Sydney Tennis Classic semi-final on Friday.

The world number four prevailed 0-6 6-4 7-6 (14-12) in a match that went the distance and will take on Paula Badosa, who beat in-form Daria Kasatkina in the other semi-final.

Krejcikova had lost five in a row against top-10 players and was soundly beaten in the first set, but she held in the second and earned the only break in the ninth game to level up. 

That set up an incredible decider, which fourth seed Kontaveit led 6-5, but she could not take the first three of her match points as Krejcikova battled valiantly to force a tie-break.

Krejcikova felt her opponent's pain as she then squandered two match points of her own when leading 6-4. 

It appeared neither player wanted to win as two more match points went begging for Krejcikova and four for Kontaveit in what turned into a real classic.

But Krejcikova eventually took her fifth opportunity to see off Kontaveit and reach a sixth WTA singles final.

"I think from both sides it was a really, really tough match," Krejcikova said. "I think we played wonderful tennis. 

"It was very, very tight, and I'm really happy that I was able to hold the nerves better and that I won this match.

"I was just playing, just trying to fight for every single ball. When I had those match points down, I was just trying to figure out how to build up the point and how to win the point."

Badosa awaits Krejcikova in Saturday's final after beating Kasatkina in a match with far fewer twists and turns.

Competing in her second semi-final in as many weeks, it was similar disappointment for Kasatkina as she fell to a 6-2 6-2 loss.

French Open quarter-finalist Badosa hit 26 winners to Kasatkina's 12 and did not look back after winning 14 of the opening 16 points.

At the Adelaide International 2, meanwhile, it will be an all-American final as Madison Keys and Alison Riske advanced past Tamara Zidansek and Coco Gauff respectively.

Riske was given a walkover win against Zidansek, who withdrew with an abdominal injury, while Keys beat compatriot Gauff in three sets.

Daria Kasatkina reached her second semi-final in as many weeks with a straight-sets victory over Garbine Muguruza at the Sydney Tennis Classic on Wednesday.

The world number 26, who was defeated by Amanda Anisimova in the Melbourne Summer Set 2 semi-finals last week, beat second seed Muguruza 6-4 6-4.

Kasatkina held throughout the opening set, landing 67 per cent of her first serves, and saw the job through in the second despite a couple of early breaks for Muguruza.

It is the Russian's first win over a top-five opponent since beating Caroline Wozniacki at the 2018 French Open.

She will now face fifth seed Paula Badosa, who saw off Olympic gold medallist Belinda Bencic 7-6 (8-6) 3-6 6-3 in an entertaining match lasting two hours and 35 minutes.

The other semi-final in Sydney will be contested between Anett Kontaveit and Barbora Krejcikova, who advanced past Ons Jabeur and Caroline Garcia respectively.

Krejcikova proved far too strong for Garcia, prevailing 6-0 6-2 in 70 minutes, while Kontaveit was in action for just 43 minutes before being handed a walkover win in her match.

Jabeur had targeted "payback" against Kontaveit after her quarter-final opponent pipped her to the final WTA Finals spot in November, but injury cost her the chance to do so.

Having lost the first set 6-4, Jabeur – who eliminated Petra Kvitova in the previous round – felt unable to continue due to a lower back injury.

At the Adelaide International 2, three of the five Americans in action made it through to the semi-finals.

Alison Riske's clash with compatriot Madison Brengle ended early due to the latter retiring with the first set level at 3-3. Tamara Zidansek awaits Riske after beating Lauren Davis 7-6 (7-4) 7-6 (9-7).

Coco Gauff and Madison Keys will meet in the other semi-final, meanwhile, following victories over Ana Konjuh and Ludmilla Samsonova in two and three sets respectively.

Ons Jabeur eliminated Petra Kvitova from the Sydney Tennis Classic and immediately set her sights on "payback" against next opponent Anett Kontaveit.

World number 10 Jabeur had lost her previous four meetings with Kvitova, but she emerged victorious on Wednesday with a 6-4 6-4 win to reach the quarter-finals.

Jabeur recovered from 3-1 down in both sets at Ken Rosewall Arena and converted half of her six break points on her way to setting up a meeting with Kontaveit.

The two will resume their friendly rivalry after Kontaveit overcame Romanian qualifier Elena-Gabriela Ruse 6-3 6-1.

Jabeur lost out to Kontaveit for the last WTA Finals spot in November and is now seeking revenge in the final warm-up event ahead of the Australian Open.

"Anett is a great player. We had our moments last year," Jabeur said. "I told her, 'You're obsessed with me, you always follow me, so stop [smiling]'.

"I know the pressure is on me, not really on her. But maybe I can get some payback for last year."

Garbine Muguruza is also through to the last eight in Sydney thanks to a 6-1 7-6 (7-4) win against Ekaterina Alexandrova.

The two-time major champion will face Daria Kasatkina, who beat Elise Mertens 6-3 6-4, for a place in the semi-finals.

Third seed Barbora Krejcikova survived a brief fightback from Jaqueline Cristian to advance 6-1 7-5, meanwhile, and Paula Badosa beat home hope Ajla Tomljanovic 6-3 6-4.

There was disappointment for in-form Elena Rybakina, who thrashed Emma Raducanu on Tuesday but had to withdraw from her clash with Caroline Garcia with a thigh injury.

At the Adelaide International 2, Coco Gauff prevailed 6-3 5-7 6-3 in her battle of the teenagers showdown with Marta Kostyuk.

Gauff is one of five Americans in the quarter-finals along with Madison Brengle, Alison Riske, Lauren Davis and Madison Keys, who beat Tereza Martincova 6-1 6-3 to advance.

Former US Open champion Sloane Stephens had to come from behind to progress against Heather Watson after almost three hours in the Indian Wells Open first round.

Stephens, who is currently ranked 73rd in the world, having been number three on the WTA Tour in 2018, triumphed 6-7 (5-7) 7-5 6-1 over Watson in two hours, 50 minutes on Wednesday.

In a see-sawing match, there were six breaks in the opening set, as Watson got the edge early on Stephens' serve at the WTA Premier 1000 event.

Stephens steadied by claiming a late break in the second to level the match, before dominating the third set.

Playing at her 10th Indian Wells Open, Stephens won seven consecutive games after the match was 5-5 in the second set.

"After the first set, that was disappointing to lose that one, but I felt like it was a battle and I was still in the match," Stephens said. "I knew I had to keep fighting and that's what I did, and I'm just really pleased to have squeaked out a win here."

KEYS ON SONG IN OPENER

Former world number seven Madison Keys moved through to the second round with a 6-0 7-5 win over fast-finishing Estonian veteran Kaia Kanepi.

American Keys won 21 consecutive points as part of a streak where she clinched the first nine games of the match, withstanding Kenapi's late push.

Keys will take on Russian ninth seed Anastasia Pavlyuchenkova for a spot in the third round.

SAMSONOVA, MARTIC, ROGERS AND PUTINTSEVA PROGRESS

Liudmila Samsonova, who made the fourth round at Wimbledon earlier this year, needed more than two hours to get past Ukrainian qualifier Kateryna Kozlova 6-4 7-6 (8-6).

Samsonova will face countrywoman and 25th seed Veronika Kudermetova in the second round.

Petra Martic won through to take on second seed Iga Swiatek with a 6-4 6-4 victory over American wildcard Katie Volynets.

Ash Barty's US Open conqueror Shelby Rogers claimed her 25th win for the year, getting past Ukrainian Anhelina Kalinina 7-6 (7-2) 6-2, while Yulia Putintseva won 7-6 (7-2) 6-1 over experienced German Andrea Petkovic to set up a showdown with fellow Kazakh player and 13th seed Elena Rybakina.

Petra Kvitova was one of a handful of seeded players to take the court at the Western and Southern Open on Monday and came away victorious against a past champion of the event. 

The 11th-seeded Kvitova defeated 2019 Western and Southern winner Madison Keys 7-5 6-4 on a rain-plagued opening day of main-draw play at the tournament outside Cincinnati, Ohio. 

The Czech saved eight of nine break points against her serve while breaking Keys three times, and that was enough to pull out the victory. 

Kvitova's countrywoman Barbora Krejcikova, the ninth seed, made her singles debut at the WTA 1000 event with a 6-3 6-2 rout of Daria Kasatkina. 

Fifteenth seed Elise Mertens also was a straight-sets winner, taking down Nadia Podoroska 6-3 6-4, while 13th seed Jennifer Brady defeated Ekaterina Alexandrova 6-3 7-6 (7-3) in a match that finished shortly before 1 a.m. local time.

Though only Krejcikova was in action Monday, the field in Cincinnati includes nine of the top 10 players in the rankings, led by Ashleigh Barty and Naomi Osaka in their first appearances since the Tokyo Olympics. 

In other matches on the first day of play, Heather Watson defeated Aliaksandra Sasnovich 6-2 3-6 6-1, while Paula Badosa outlasted Petra Martic 4-6 6-4 7-6 (11-9) in a two-hour, 34-minute marathon. 

Yulia Putintseva breezed past Zhang Shuai 6-2 6-0, Jelena Ostapenko beat Tamara Zidansek 7-5 6-1 and Jil Teichmann downed Sorana Cirstea 6-2 6-0. 

Angelique Kerber beat Maria Sakkari 6-2 6-2, with Alison Riske matching that scoreline in a defeat of Leylah Fernandez.

Shelby Rogers won 6-4 2-1 when her countrywoman Danielle Collins retired with an injury. 

Karolina Muchova was a casualty in the first round of the National Bank Open as she was stunned by Oceane Dodin in Montreal on Monday.

The 14th seed was undone by the French qualifier despite Dodin sending down 10 double faults.

The 6-3 1-6 6-2 success was Dodin's first over a top-25 player this season.

Former U.S. Open finalists and 16th seed Madison Keys was also a first-round casualty, going down 6-3 6-3 to Canadian Rebecca Marino.

Toronto-born Marino, currently ranked 220th in the world, won in one hour and six minutes, converting four of her eight break points, while she saved four from five too.

However, there were no such problems for Ons Jabeur, the 13th seed strolling to a 6-1 6-3 victory over Clara Burel.

Eleventh seed Maria Sakkari also had a routine day, her opponent Marie Bouzkova unable to continue with Sakkari ahead 6-4 3-1.

An Olympic gold medallist in the doubles at Tokyo 2020, Katerina Siniakova had more to celebrate in the singles with a 6-1 6-3 win over long-time rival Jelena Ostapenko.

Elsewhere in the draw, Paula Badosa, Sorana Cirstea, Amanda Anisimova, Nadia Podoroska and Fiona Ferro all progressed.

World number 26 Madison Keys was one of three seeded players to be eliminated in the second round of the Silicon Valley Classic in San Jose on Wednesday.

The American third seed was beaten by China's Zhang Shuai 7-5 7-6 (7-5) in one hour and 39 minutes.

Keys sent down 7-1 aces but Zhang, ranked 51st in the world, was excellent on return, converting four of her 11 break points.

Fourth seed Daria Kasatkina was also in danger after losing the first set but rallied to win 3-6 7-5 6-3 over France's Caroline Garcia.

"It was a tough match. From my point of view, I think the level of the game was very good, and I'm really happy that I was able to turn the match in the second set," Kasatkina said in the on-court interview.

Ninth seed Alison Riske was emphatically beaten by Croatian Ana Konjuh 6-1 6-4 in one hour and 13 minutes, while sixth seed Petra Martic bowed out to Poland's Magda Linette 7-5 7-6 (7-5).

Belinda Bencic got her grass-court season under way with a battling victory over qualifier Jule Niemeier in the first round of the inaugural bett1 Open.

Fifth seed Bencic came from a set down to beat 167th-ranked German Niemeier 4-6 6-4 7-5 in Berlin on Monday.

The 21-year-old Niemeier was playing her first professional match on grass and gave a great account of herself against the world number 12, who needed two hours and 12 minutes to secure her place in the second round.

Bencic secured the only breaks in the second and third set to ensure she will face Petra Martic or Asia Muhammad in round two.

Madison Keys progressed in straight sets, getting the better of Polish qualifier Magdalena Frech 6-3 6-4.

The American, a winner of two WTA singles titles on grass, struck 19 winners as she set up an encounter with top seed Aryna Sabalenka.

There were also first-round victories for Alize Cornet and Ekaterina Alexandrova earlier in the day over Amanda Anisimova and Anna Kalinskaya respectively.

Serena Williams said her serve was the key to battling past Mihaela Buzarnescu 6-3 5-7 6-1 in the second round of the French Open on Wednesday.

The win improved Williams' second-round record in grand slams to 74-2, her only defeats at this stage having come against sister Venus Williams when Serena made her major debut at the 1998 Australian Open, and against Garbine Muguruza seven years ago at Roland Garros in Paris.

Serena Williams won 75 per cent of the points played behind her first serve and saved five of the seven break points she faced in the French capital midweek.

"I felt it was pretty good today," Williams said of her serve. "But I've been practicing my serve a lot. I've been playing unbelievable on my serve in practice. The other night was, 'wow'. I'm glad it came better today.

"My coach told me it's good that I'm doing it well in practice because eventually it will be good in the match.

"I had some really good chances in the second set to win that. If I would have won just one point here or there, like four or five times, it would have been a different second set.

"I know going into the third I just had zero in on those one important points. If I could just take those, it would be an easier time for me."

The 39-year-old will continue her quest for a fourth Roland Garros title and record-equalling 24th slam crown against compatriot Danielle Collins, who beat Ukrainian qualifier Anhelina Kalinina 6-0 6-2.

"She's been playing well," Williams added. "She's also a really awesome person off the court. I love seeing her in the locker room.

"Ideally, it would be great if we didn't have to play each other because I always want her to do super well."

BENCIC DUMPED OUT BY KASATKINA

Belinda Bencic – the 10th seed – was dumped out by Daria Kasatkina 6-2 6-2, meaning there are no top-20 players left in the bottom quarter of the draw.

Bencic joined world number two Naomi Osaka, Bianca Andreescu and Kiki Bertens in departing the tournament after a dismal performance against Kasatkina, who will play in the third round of a major for the first time since Wimbledon in 2018.

Kasatkina's serve was in rude health, with the Russian and 2018 French Open quarter-finalist never facing a break point and racking up eight aces.

"A lot has changed between 2018 and now," said Kasatkina. "There was one amazing year for me, which was important in a good and in the bad way.

"I learned a lot, and I think I became a little bit different, maybe more experienced, a bit more serious. Let's say I understand more why I'm winning or why I'm losing.

"At that time everything was just going with the wave, and I was not thinking that much. Now I'm analysing more of what's going on in the situation I'm in. Getting maybe a bit more mature."

The only player left in that quarter who has previously reached a grand slam semi-final is 20th seed Marketa Vondrousova, who breezed past Harmony Tan 6-1 6-3. 

SABALENKA SEES OFF COMPATRIOT SASNOVICH

Third seed Aryna Sabalenka booked her spot in the third round with a 7-5 6-3 win over fellow Belarusian Aliaksandra Sasnovich, despite tallying 34 unforced errors.

Sabalenka, who has the second-most tour-level wins this season with 27, said: "I'm really proud of myself that I was fighting no matter what, kind of trying to find my rhythm. I'm really happy with this win. It was a tough battle.

"I would say I definitely feel better this year, kind of believe that I can do well here on the clay court. I feel better and really happy to be here, to compete here."

Sabalenka will now face 31st seed Anastasia Pavlyuchenkova in the next round after the Russian defeated Ajla Tomljanovic 6-2 6-3. 

There were also wins for two-time grand slam champion Victoria Azarenka, who overcame Clara Tauson 7-5 6-4, and Madison Keys, who beat Leylah Annie Fernandez 6-1 7-5.

Garbine Muguruza eased into the second round of the Internazionali BNL d'Italia on Tuesday thanks to a comfortable victory over lucky loser Patricia Maria Tig, though Belinda Bencic was the biggest casualty on a rain-interrupted day.

Spaniard Muguruza was due to face Anastasia Pavlyuchenkova until the Russian withdrew due to an abdominal issue, giving Tig a reprieve and the chance of an upset.

But Muguruza won all but three games in a comprehensive 6-1 6-2 victory that required little more than an hour on court as the former world number one went to 22-6 for the season.

Conditions were not great as drizzle persisted for much of the match, but Muguruza was grateful to progress after a generally testing day.

"It was a weird day," the 12th seed said afterwards. "I woke up [and the weather was] sunny, had an opponent. Then it turned out I had another opponent and it was raining the whole match. We had a little bit of everything!

"But, Rome, it's such a familiar tournament. I played here so many times, I've had nice matches. I love this clay, the red clay. It's familiar to me. I'm just looking forward to getting as many matches as possible."

Bencic will not be joining her in the next round, as she became the highest seed to be eliminated on the day in a 6-3 6-4 defeat to Kristina Mladenovic.

The two played each other under two weeks ago in the first round of the Madrid Open, with Bencic victorious, but Mladenovic got her revenge as she capitalised on her opponent's seven double faults.

Like Tig, Sloane Stephens was also competing as a lucky loser as she came up against compatriot Madison Keys, though the outcome was no different.

Keys claimed only her second win in six meetings with Stephens but had to come from behind as she eventually clinched it 4-6 6-2 7-5 after two-and-a-half hours on court to set up a clash with 15th seed Iga Swiatek.

Elise Mertens, the 14th seed, was also dumped out of the competition, losing out 4-6 6-2 6-3 to Veronika Kudermetova, whom she had beaten in straight sets in their three WTA Tour contests before this one.

Veteran Kazakh Yaroslava Shvedova, ranked 665 in the world, awaits top seed Ashleigh Barty after the 33-year-old showed character to fight back and beat Martina Trevisan 0-6 7-6 (7-4) 7-6 (8-6), while Nadia Podoroska set up a second-round clash with Serena Williams after seeing off Laura Siegemund 2-6 7-6 (7-3) 6-1.

Ash Barty won her first match on clay since reigning supreme at the 2019 French Open as the world number one rolled into the Volvo Car Open round of 16.

Barty – who last featured in a clay-court match en route to Roland Garros glory almost two years ago amid the coronavirus pandemic – made light work of Misaki Doi 6-2 6-1.

Miami Open champion last week, top seed Barty continued where she left off at the WTA 500 event on Wednesday, closing out proceedings in just over an hour in Charleston.

"I had to use it as an opportunity to try and build some comfort," Barty said. "I think having a couple days between Miami and playing this first match was important, to have my body rest, but to also try and prepare to change surfaces. It was a very quick turnaround, but I felt great out there tonight."

Barty – who now boasts a 15-2 win-loss record in 2021 – will next face Shelby Rogers after she outlasted 13th seed Amanda Anisimova 1-6 7-5 6-4.

As for second seed Sofia Kenin, the 2020 Australian Open champion slumped to a shock 4-6 6-3 6-4 defeat against Lauren Davis midweek.

World number four Kenin – runner-up at last year's French Open – eased to the first set but fellow American Davis, ranked 79th in the world, changed tactics to fine effect.

"I was a bit uncomfortable so I just really dug deep and really started to think about how to beat her and I found that heavy deep balls were not her favourite," the 27-year-old Davis said.

"Being on clay, the ball bounces high, pushing girls back, so it's very effective."

Kenin took a medical timeout at 3-0 down in the deciding set but, despite reeling off the next three games, she was unable to see Davis off as her 2021 woes continue.

Davis now heads into another all-American clash with teenage sensation Coco Gauff – who came from 1-3 down in the third to defeat Liudmila Samsonova 4-6 6-1 6-4 in an absorbing two-hour contest.

Belinda Bencic – the fifth seed – crashed out as Paula Badosa claimed the first top-20 win of her career following a 6-2 6-7 (2-7) 6-1 success.

Badosa will face Caty McNally in the last 16 after the 19-year-old American beat Anastasija Sevastova 7-6 (7-3) 2-6 6-4.

Seventh seed Elise Mertens was another big name to depart as Alize Cornet prevailed 7-5 6-3, although 15th seed Veronika Kudermetova and 12th seed Ons Jabeur progressed in with the minimum of fuss.

Former US Open champion Sloane Stephens, meanwhile, topped eighth seed Madison Keys 6-4 6-4.

Seeds were even more vulnerable at the Copa Colsanitas in Bogata, including the top-seeded Saisai Zheng who was dispatched 6-4 6-1 by Stefanie Voegele.

Zheng's compatriot Yafan Wang, seeded eighth, went down 6-3 6-3 to Viktoriya Tomova.

Arantxa Rus and Jasmine Paolini, the third and sixth seeds respectively, lost in three to Spanish duo Nuria Parrizas Diaz and Lara Arruabarrena.

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.

Madison Keys is set to miss the Australian Open after testing positive for coronavirus.

The 2017 US Open runner-up announced on Thursday that she contracted COVID-19 before she was due to fly out for the first grand slam of the year.

Keys did not state she will definitely miss the major, which starts on February 8, but it appears the American will not make the trip to Melbourne.

The American wrote on Instagram: "Hi everyone, I wanted to let you know that I unfortunately tested positive for COVID-19 before I was supposed to fly to Australia.

"I'm very disappointed to not be able to play in the coming weeks after training hard in the off-season and knowing Tennis Australia and the tours did so much to make these events happen.

"I am self-isolating at home and will continue to follow all the necessary health precautions. I look forward to being back on tour next month."

It was revealed earlier in the day that three-time major winner Andy Murray has also tested positive for the virus, but still hopes to play in the Australian Open.

Meanwhile, world number 50 Tennys Sandgren was cleared to board a flight from the United States bound for Melbourne despite revealing he returned a new positive coronavirus test this week. 

The American, twice a quarter-finalist at Melbourne Park, initially posted to social media on Wednesday that he had tested positive for the virus for a second time. 

Although his first instance of having the illness was recorded in November, the 29-year-old's participation in the tournament appeared to be in doubt. 

But as he continued to update followers through the day, it emerged he had been allowed to board his flight. 

Players will only be allowed into Australia with proof of a negative test just prior to departure, or with approval to travel as a recovered case at the complete discretion of an Australian government authority.

Anyone wanting to travel out for the tournament who previously tested positive is required to provide additional and highly detailed medical information as proof they are a recovered case and no longer infectious or a risk to the community.