Rafael Nadal's United Cup campaign began with defeat against Cameron Norrie as Great Britain established a 2-0 lead over Spain in Group D.

The 22-time grand slam winner surrendered a first-set lead before going down 3-6 6-3 6-4 against the world number 14, who secured his first victory in five meetings.

Norrie, who became only the second Briton after Andy Murray to beat the Spaniard, set the tone for his team, with Katie Dart also coming from behind to deny Nuria Parrizas Diaz 3-6 6-1 6-2 later on.

Meanwhile, Germany's Alexander Zverev lost in straight sets on his return to ATP action, going down 6-4 6-2 to Jiri Lehecka of the Czech Republic, who went 2-0 up in the tie after Marie Bouzkova defeated Jule Niemeier 6-2 7-5.

World number one Iga Swiatek got Poland off to a flying start against Kazakhstan in Brisbane with a commanding 6-1 6-3 victory over Yulia Putintseva, but defeat for Daniel Michalski against Timofey Skatov leaves the Group B tie finely poised.

Brazil enjoyed a flawless start against Norway in Group E. Beatriz Haddad Maia was a 6-4 6-2 winner over Malene Helgo, and Felipe Meligeni Alves overcame Viktor Durasovic 6-3 6-3.

The spoils were shared between Belgium and Bulgaria in Group A with Alison van Uytvanck beating Isabella Shinikova, before David Goffin was seen off by Grigor Dimitrov 6-4 7-5.

Croatia closed the day with a pair of victories against Argentina in Group F as Donna Vekic and Borna Coric defeated Maria Carle and Francisco Cerundolo respectively.

Maria Sakkari sealed victory for top-seeded Greece over Bulgaria in the United Cup with a straight sets win over Viktoriya Tomova.

Team-mates Stefanos Tsitsipas and Despina Papamichail had already won their matches on Thursday, and Sakkari's 6-3 6-2 triumph gave Greece an unassailable 3-0 lead.

Michail Pervolarakis was defeated by Dimitar Kuzmanov in the final singles match between the nations, but Tsitsipas and Sakkari teamed up to earn Greece a 6-4 6-4 success in the doubles encounter to end on a high.

World number 16 Matteo Berrettini helped Italy topple Brazil by overcoming Thiago Monteiro 6-4 7-6 (9-7).

That gave Italy a 2-1 lead, and Lucia Bronzetti finished the job by demolishing Laura Pigossi in straight sets, with Brazil powerless to overturn the deficit despite Berrettini and Camilla Rosatello's defeat in the doubles match.

US Open semi-finalist Frances Tiafoe clinched a win for the United States over the Czech Republic after opponent Tomas Machac retired with an ankle injury with the score at 6-3 2-4.

Petra Kvitova had defeated Jessica Pegula 7-6 (8-6) 6-4 in the third singles match to give Czech Republic hope, but Tiafoe's win settled the contest before Pegula and Taylor Fritz joined up for success in the doubles.

Great Britain were 3-2 victors over Australia despite a pair of defeats on day two in Sydney.

Cameron Norrie's triumph over Nick Kyrgios' replacement Alex De Minaur on day one had helped Great Britain to a 2-0 lead over the hosts, and Harriet Dart prevailed over Maddison Inglis to wrap up the victory.

Dan Evans was then beaten 6-3 7-6 (7-3) by Jason Kubler before Dart and Jonny O'Mara fell to defeat in the doubles, but Great Britain's strong start saw them through.

France and Switzerland completed 5-0 sweeps of Argentina and Kazakhstan respectively, with Caroline Garcia winning both her singles and doubles matches in straight sets while Stan Wawrinka saw off Alexander Bublik 6-3 7-6 (7-3).

Nick Kyrgios accused Australia co-captain Lleyton Hewitt of throwing him "under the bus" following his decision to withdraw from the United Cup.

The 2022 Wimbledon finalist, who has been struggling with an ankle injury, was due to line up alongside the likes of Alex De Minaur and Jason Kubler in the inaugural edition of the team event.

However, Kyrgios surprised team-mates with his decision to pull out of the event, with the 27-year-old switching his focus to achieving full fitness for next month's Australian Open.

Hewitt was unaware of Kyrgios' withdrawal until his public announcement and said he needs to improve his communication skills.  

Kyrgios' withdrawal was followed by that of Ajla Tomljanovic, who pulled out of her match against Great Britain's Harriet Dart due to a knee injury.

Kyrgios responded to a Twitter post about the news, questioning whether co-captain Sam Stosur would respond the same way Hewitt did.

"Mmm I wonder if Stosur will throw her under the bus like our captain did for me... 'hard to prepare when you don't know what's going on'," Kyrgios wrote.

Australia suffered a 3-2 defeat to Great Britain in their Group D meeting, although they will have another chance to progress to the knockout stage when they face Spain next week.

Stefanos Tsitsipas opened his United Cup campaign with a comeback victory over Grigor Dimitrov in Perth.

ATP world number four Tsitsipas is one of the headline names in action at the event, which is acting as a warm-up tournament for the Australian Open.

After going a set down to his Bulgarian opponent in his first game of the inaugural tournament, Tsitsipas hit back with a strong second set before holding his nerve in a tense tie-break in the decider, securing a 4-6 6-2 7-6 (7-4) win.

Tsitsipas's team-mate Despina Papamichail continued Greece's strong start, also coming from a set down to beat Isabella Shinikova 3-6 6-4 6-1.

Great Britain opened with a pair of victories, Cameron Norrie and Katie Swan earning straight sets triumphs over their Australian counterparts in Sydney.

Norrie, who was initially set to play Nick Kyrgios prior to the Wimbledon finalist's withdrawal due to an ankle injury, eased to a 6-3 6-3 victory over Alex De Minaur, while Swan defeated Zoe Hives. 

The United States are also taking a 100 per cent record into day two of the tournament, after Taylor Fritz and Madison Keys overcame Jiri Lehecka and Marie Bouzkova respectively, while France pair Arthur Rinderknech and Alize Cornet got off to winning starts against Argentina's Francisco Cerundolo and Maria Lourdes Carle.

In Brisbane, Swiss hope Belinda Bencic secured a 7-6 (7-0) triumph over Yulia Putintseva of Kazakhstan and Beatriz Haddad Maia, the Brazilian world number 15, dispatched Italy's Martina Trevisan 6-2 6-0.

Nick Kyrgios has withdrawn from the United Cup on the eve of the inaugural edition of the tournament, with Australia team captain Samantha Stosur admitting "it's news to all of us."

The 2022 Wimbledon finalist, who has been struggling with an ankle injury, was due to line up alongside the likes of Alex De Minaur and Ajla Tomljanovic in the new team event.

However, Kyrgios surprised team-mates with his decision to pull out of the event, in which Australia face Great Britain in their opening match on Thursday, reportedly switching his focus to achieving full fitness for next month's Australian Open.

"I'm not going to speak for Nick’s summer, we've got to leave that for him," Stosur said at a press conference. "He was here. We literally just found out 10 minutes ago, so it's obviously news to all of us.

"But we just move forward now. We're all happy to be here and keen to get out there. Now that's out there, and we move forward with the placings of the team and do our best on the day.

"As far as the men's side of this team goes, we're in very capable hands still, so I'm not concerned that our chances have just diminished greatly or anything like that. We're out here to do everything we can possible to try and win this competition."

De Minaur added: "We've all just heard. Ultimately, we're just going to get ready. We’ve got a great team, and we're all going to be out there doing our best. So ultimately, the only thing that changes is match-ups and that's about it."

Tennis icon Venus Williams will compete in her 22nd Australian Open in January after it was announced on Sunday she had been awarded a wildcard entry.

Williams, 42, is a seven-time grand slam singles champion, but she only played four competitive matches in 2022, losing all four.

A five-time Wimbledon winner with two US Open titles on the singles side, Williams is also one of the sport's most decorated doubles players, collecting another 14 grand slam doubles titles, including four in Australia.

She won the Australian Open doubles in 2001, 2003, 2009 and 2010, while making the singles final in both 2003 and 2017.

In the press release announcing her wildcard, Williams confirmed her plans to compete once again in Melbourne.

"I am very excited to be returning to Melbourne to compete at the Australian Open in January," she said.

"I've been competing in the country for over 20 years now and the Australian community has always supported me wholeheartedly.

"It will be an honour to play for the fans again and I'm looking forward to making more memories at the tournament this year."

It remains to be seen if she will be joined by her sister, Serena, who is a seven-time singles champion at the event and Venus' partner for her four doubles successes.

After her exit from the US Open, Serena heavily implied she was weighing up another go down under, saying "I always did love Australia".

Emma Raducanu is working with a new coach as she heads towards the 2023 season, reports said on Friday.

The 2021 US Open winner, who turned 20 in November, has had a growing list of coaches and is seeking the right formula to make an alliance successful.

She has turned for now to German Sebastian Sachs, a 30-year-old who previously worked with Victoria Azarenka, as a member of the Belarusian's team, before becoming the main coach of Julia Goerges and latterly Belinda Bencic.

Olympic champion Bencic recently appointed Dmitry Tursunov, who had been working with Raducanu, and Sachs has headed in the opposite direction by joining up with the British youngster.

As well as Russian former ATP top-20 player Tursunov, Raducanu has had coaching spells under the tutelage of Nigel Sears, Andrew Richardson, Torben Beltz and the Lawn Tennis Association's Iain Bates in the past two years.

Raducanu and her team have yet to formally announce Sachs' role, but reports have indicated he has been with her this week in Abu Dhabi. Her management have yet to confirm whether this is a trial or a full-time appointment.

The one-time grand slam winner had a match on Friday against Ons Jabeur at the Mubadala World Tennis Championship, an exhibition event, losing 5-7 6-3 10-8 to the 2022 Wimbledon and US Open runner-up.

After parting company with Raducanu, Tursunov said getting the best out of the Briton would be "minimum a one-year project but... probably a two-and-a-half-year project to be on the safe side", and reasoned that her game remained "very raw".

"It's going to take some time, but as I said to her and to pretty much everyone on her team: I think you just need to have one voice and just try that for a bit," Tursunov said.

Raducanu has not reached a final since her dazzling Flushing Meadows victory, and she finished the 2022 season at 76th in the WTA rankings.

Serena Williams may return to the court "one more time," former world number two Tommy Haas believes.

The 23-time grand slam singles champion Williams declared her intention to "evolve" away from tennis prior to the US Open in September, with many thinking her third-round defeat to Ajla Tomljanovic signalled the end of her illustrious career.

Although, the 41-year-old hinted she may return in a recent interview with Jimmy Fallon, suggesting she may follow the example of another American sporting great.

"Tom Brady started an amazing trend," she said when asked if her competitive career may resume. "That's what I want to say."

Speaking to Eurosport Germany's tennis podcast Das Gelbe vom Ball, Haas said: "Serena had an incredible, long and strong career. 

"But I have the feeling that she is going to come back and say, 'I'm going to play one more time.' 

"She came so close to playing really well again and going far, so I think deep down it really annoys her.

"She might really be thinking about whether she wants to try again. I may be wrong because I'm not that close [to her].

"It will mostly depend on how it looks mentally, how she feels physically and whether she has the desire to torture herself like that again after achieving so much."

Carla Suarez Navarro has announced she is pregnant, with the Spanish former tennis star who overcame cancer expressing her "tremendous joy" and "great pride."

Now 34, Suarez Navarro was diagnosed with Hodgkin lymphoma in September 2020, just months after announcing her intention to retire.

She delayed that retirement and, after being given the all-clear in April 2021, began a farewell tour at that year's French Open that included appearances at Wimbledon, the US Open, the Olympic Games and the Billie Jean King Cup.

Having left competitive tennis behind at the end of the 2021 season, Suarez said she and her partner Olga Garcia were thrilled to announce the pregnancy, with their baby due in June.

Garcia, 30, is a footballer who has played for the Barcelona, Atletico Madrid and Spain women's teams.

They said in a shared statement on Instagram: "A new stage that we really wanted to experience. Let's grow the family! Excited and happy to face this big moment. Very soon we will be one more."

Both were showered with messages of congratulations and love, from the likes of Manchester United goalkeeper David de Gea and tennis names including Caroline Wozniacki, Garbine Muguruza, Paula Badosa and Sara Errani.

Suarez Navarro explained, in a statement reported by Spanish media: "We wanted to announce that I am three months pregnant. It's already 12 weeks of tremendous joy to bring a new life into the world.

"Both Olga Garcia, my partner, and I feel an enormous responsibility, a great pride for having taken this step, and we were excited to share it with all of you.

"This Tuesday, we went to perform the first trimester ultrasound, to verify that the pregnancy is progressing on the right track. Fortunately, the medical team has confirmed that the gestation process is developing completely normally.

"It is fantastic news for us and fills us with hope for the near future."

The former WTA player, who reached a career-high world ranking of sixth, added: "After my retirement from sports, with both of us still young, we thought it was the ideal time to face a process that fills us with joy and enthusiasm.

"We are very excited with what we are going through and with all the experiences that we hope to live soon."

Ash Barty is adamant she "absolutely fulfilled every ounce" of her tennis aspirations following her shock retirement earlier this year.

The three-time grand slam winner was at the peak of her powers when, in March, she made the surprise decision to call time on her tennis career at the age of 26.

The former world number one and reigning Australian Open champion later revealed to friend and former player Casey Dellacqua that she was 'spent' and no longer had the 'physical drive' or 'emotional want'.

Following her triumph at Melbourne Park, making her the first home women's singles champion since Chris O'Neil in 1978, Barty became the first player to win the Newcombe Medal on five occasions.

She maintained her record of having won the award, the highest individual honour in Australian tennis, every year since it was first presented in 2017.

"This has obviously been a very big year in my career and in my life," said Barty, who beat Wimbledon runner-up Nick Kyrgios, US Open mixed doubles champion Storm Hunter, Ajla Tomljanovic and Alex De Minaur to the accolade.

"We've had exceptional change, we've had an amazing year of celebrating a journey of not only myself, but my team, and there is so much to be proud of.

"I stand here very proudly knowing that I absolutely fulfilled every ounce that I could to this beautiful sport that brought me so much more than I could have ever dreamt."

Carlos Alcaraz pinpointed Iga Swiatek as a hot shot example to follow as the world number one looks to successfully defend top spot in the ATP rankings.

Spaniard Alcaraz enjoyed a hugely impressive 2022 season, winning five titles including a first grand slam at the US Open.

The 19-year-old subsequently became the youngest number one in ATP history, as well as the youngest player to top the year-end rankings.

It has also been a dominant year for Swiatek, who landed eight titles including the French Open and US Open, while also embarking on a 37-match winning streak – the longest this century on the WTA Tour – and registering 22 'bagel' sets.

Alcaraz, who knows there will be greater expectations on him delivering the goods, hopes to follow in the footsteps of the runaway WTA leader.

"I see her year has been incredible," Alcaraz told Arab News. "She broke a record for the longest winning streak [this century]. It's amazing,

"I wish to be like her, to not lose the number one [ranking]. But I think it's almost impossible. I'm going to lose it, but the point is to recover it and stay there at number one as much as I can."

He added: "Obviously yes, all the people want to beat the number one in the world. I could feel that after the US Open, everyone had a target on me and everyone wanted to face me on court. That's what I have to be prepared for."

Despite an incredible year, Alcaraz admitted his achievements are yet to truly hit home.

"It sounds like a dream for me," he said. "Honestly, there are so many times I think about this year, about my position right now, and I still can't believe it. I'm thinking: 'Is this real? I’m number one in the world?' I'm dreaming. It's something I have to realise someday."

Karolina Pliskova will reunite with coach Sascha Bajin for the 2023 season, she has announced.

The pair previously began working together in November 2020, with Pliskova going on to enjoy a successful 2021 season that saw her reach the Wimbledon final, as well as the title matches in Rome and Montreal.

However, they parted in July 2022 after the former world number one, who missed the start of the campaign with a hand injury, suffered a surprise second-round Wimbledon exit, having also fallen at that stage of the French Open.

Despite reaching the US Open quarter-finals under the guidance of Czech compatriot Leos Friedl, Pliskova has slipped to 31st in the WTA rankings, but German coach Bajin is confident her fortunes can improve.

"I am returning mainly because I still believe I can help Karolina with my insights," Bajin said.

"Her game has gradually improved since her hand injury and, in my eyes, she has proven that she can still compete with the best in the world.

"We will want to build on these performances and that is why we have decided to renew our connection. I can't wait to sit in her corner again."

Of Friedl, Pliskova added: "Many thanks to Leos, who willingly started working with us immediately. I think that under his guidance, we managed to get some interesting results."

Legendary tennis coach Nick Bollettieri has died at the age of 91.

The American, who coached the likes of Andre Agassi, Serena Williams, Maria Sharapova and Boris Becker, passed away on Sunday.

He founded the Nick Bollettieri Tennis Academy, now the IMG Academy, and long since gained a reputation of being one of the most iconic coaches in the sport.

Tommy Haas, who was also coached by Bollettieri, paid an emotional tribute to him on Monday.

The German posted on Instagram: "So many memories, I am not sure where to begin. Nickiiiii, that's how I have called you for the longest time.

"Thank you for your time, knowledge, commitment, expertise, the willingness to share your skill, your personal interest in mentoring me and giving me the best opportunity to follow my dreams.

"You were a dreamer and a doer, and a pioneer in our sport, truly one of a kind.

"I surely will miss you around the academy, our tennis talks, miss showing of [sic] your tan, white teeth and body fat, miss watching you do Tai Chi, miss playing golf with you watching you try to cheat, eating a Snickers bar and running for the bushes, and hearing all about your plans even at the age of 91.

"Thanks again for everything……..

"RIP Nickiiiii."

Monica Seles and Jim Courier were among the other players who were coached by Bollettieri.

Emma Raducanu felt "extremely grateful" after being made an MBE for her services to tennis.

The 20-year-old was presented with the honour by King Charles III in a ceremony at Windsor Castle on Tuesday.

It comes 14 months after Raducanu's fairytale triumph at the US Open, where she became the first British female grand slam champion since Virginia Wade's Wimbledon victory in 1977.

The then 18-year-old was also the first qualifier to land a major after her straight-sets her win over Leylah Fernandez in the championship match at Flushing Meadows.

In a statement released via her agent, Raducanu said: "It's been great to receive my honour today from his Majesty the King - I feel extremely grateful."

Raducanu did not enjoy a fruitful season in 2022, as she failed to win a trophy or progress beyond the second round in any of the grand slams.

Her deepest run in a tournament came in September, when she reached the semi-finals of the Korea Open, but she had to retire hurt from a semi-final tie with Jelena Ostapenko.

Roger Federer believes the intense tennis tour schedule can have a negative impact on the mental health of players.

Federer, now retired, won 20 grand slam titles between 2003 and 2018 before stepping away from the sport in September of this year, and he is well aware of the challenges players face.

A number of big-name stars have spoken out about their mental health, including Naomi Osaka and Nick Kyrgios, and Federer feels the packed tennis calendar does not help players.

"When players retire at a super young age, I totally understand it," Federer told a press conference in Tokyo. "The tour is tough... travel, practice, jetlag.

"Nobody is allowed to say, 'Oh, I'm tired today', because it looks like you're weak, and that's why players end up having sometimes mental problems.

"You're supposed to show strength. But we're also not machines, we’re also just human beings."

Federer played on the tour for 25 years before calling it a day, and he is making the most of being able to finally relax, saying: "As a tennis player you're always thinking about your next practice, your next match. It never lets you go.

"I don't think I was that much aware of it, how much that thought is always there, and it rides with you, until you retire and then you realise that stress all drops away."

He pointed to doping tests, and the fact players must constantly make authorities away of their whereabouts.

"We have to fill out the doping forms every single day, one hour during the day, where you are," Federer said. "You're always aware in the back of your head, they could be coming any moment, especially in that hour.

"Once that all drops away you actually feel quite lighter, relieved that you can actually live normally again after 25 years."