Top seed Victoria Azarenka overcame a lapse of concentration to defeat Ana Ivanovic 6-0, 4-6, 6-3 and reach the final of the Carlsbad Open on Saturday.
Andy Murray stayed on course for a second Wimbledon title while setting setting up a semi-final showdown with Roger Federer.
Top seed Maria Sharapova was stretched by Serbia's Ana Ivanovic before she claimed a 7-6 7-5 win to reach the semi-finals of the Linz Open on Friday.
The 13th seeded Czech proved too strong for Serb, who lifted the Suzanne Lenglen Cup in 2008, winning 7-5, 6-4.
Third seed Jelena Jankovic had to work very hard on Friday to quell the challenge of Czech Lucie Safarova 5-7 7-6 6-2 and reach the fourth round at Wimbledon.
Seven-times grand slam champion John McEnroe called Nadal's latest injury "extremely disappointing". "We've seen him play for many years and it's always been a concern about how his knees would hold up," the American told Eurosport in his daily spot. "After last year, we all hoped he would be able to get his health and fitness back and get his game together and it looked like that was happening. "We all know how much he wanted (title) number 10 and we were looking forward to seeing play Novak in the semis." Former French Open champion Mats Wilander said the decision had been a no-brainer for Nadal.
Defending champion Nadia Petrova was also shown the door in the quarter-finals of the German Open.
Australia hot-headed tennis star Nick Kyrgios was handed a $16,500 fine on Thursday after he tanked a match and got into an argument with fans at the Shanghai Masters.
The Frenchwoman went down to rising Serb Ana Ivanovic 6-3, 7-5 at the Sydney International.
Rafael Nadal eased past Spanish compatriot Nicolas Almagro 6-3, 6-1 to reach the Barcelona Open third round on Wednesday as he began his bid for a ninth title on the clay in the Catalan capital.
A summary of sports events and sports persons, who made news on Friday
There is no let-up for Roger Federer as he prepares for his 12th consecutive appearance at the ATP's season-ending extravaganza.
Novak Djokovic beat Tomas Berdych 7-6 (3), 7-6 (8) in the quarter-finals of the Paris Masters on Friday to claim his 20th consecutive win and stay on course for an unprecedented third title in a row at the event.
Inter Milan are on the verge of signing Manchester United captain Nemanja Vidic, with president Erick Thohir saying on Thursday that the deal was almost finalised.
Bulgaria's Grigor Dimitrov upset top seed and defending champion Milos Raonic of Canada at the Brisbane International on Saturday to set up a title clash against Japan's Kei Nishikori.
The second seed dismissed a challenge from rising Serb teenager Ana Ivanovic to reach the fourth round of the Australian Open.
Ash Barty beat eighth seed Kiki Bertens of the Netherlands 6-3, 3-6, 7-6(7) in Beijing to seal her spot in the final of the China Open on Saturday.
The doctors at the ongoing Australian Open tournament are reportedly confident that the tennis stars can cope with the extreme heat over the next four days.
The American ace has won all 10 semi-finals she played this season and never failed to reach the title match in Zurich in the six years she has played the event.
Novak Djokovic lost his momentum in the second half of last season and was toppled as the world number one by Andy Murray because his work-rate dropped, the Serbian's former coach Boris Becker said on Wednesday. Speaking a day after the two terminated their cooperation by mutual consent, German Becker said Djokovic's need to spend more time with his family had derailed him on the court.
Former champion Janko Tipsarevic has confirmed his participation for the USD 450,000 Aircel Chennai Open to be held here from January 5 to 11.
Stuns World No 1 Djokovic to win 'biggest title of career'
'A 2018 murder may lead to shifts in the geopolitical order and impact at least one monarchy,' says Devangshu Datta.
Djokovic, the ninth seed, was originally scheduled to play Australian Open semi-finalist Chung Hyeon but the 22-year-old South Korean withdrew with a back injury about an hour before the match was due to start.
Novak Djokovic has denied an Italian media report he deliberately lost a match in 2007 that has been linked to a wider scandal involving alleged corruption in tennis. The 28-year-old world number one, who easily beat French teenager Quentin Halys on Wednesday to advance to the Australian Open third round, was asked about a report in Italian newspaper Tuttosport that he had deliberately lost to now-retired French player Fabrice Santoro at the Paris Masters. "It's not true," the Serb said with a shrug and shake of his head. "What it is to say? I've lost that match. "Anybody can create a story about that match or for that matter any of the matches of the top players losing in the early rounds, I think it's just absurd." "You can pick any match that you like that the top player lost and just create a story out of it."
The Belgian was beaten by Russia's Svetlana Kuznetsova in the semi-finals of the Warsaw WTA claycourt event.
Pliskova will be guaranteed toppling Germany's Angelique Kerber if she prevails against Halep who would need to go on and take the title to seize the top ranking.
