MADRID - World number one Rafael Nadal stormed into the semi-finals of the Madrid Masters on Friday with his 17th consecutive win over Tomas Berdych, 6-4, 6-2. Maria Sharapova also booked her place in the last four of the Madrid Open with a three-set win over Li Na, but top seed and reigning champion Serena Williams was forced to pull out of the tournament due to a thigh injury.Despite coming into the tournament with doubts following surprise defeats to David Ferrer and Nicolas Almagro in recent weeks, Nadal has looked in fine form in the Spanish capital as he has cruised into the last four without the loss of a set. The 13-time Grand Slam champion will meet compatriot Roberto Bautista Agut or Colombia's Santiago Giraldo on Saturday for a place in the final.Williams was due to face Petra Kvitova in the quarter-finals but pulled out due to a thigh injury she had been carrying since sweeping aside Swiss teenager Belinda Bencic in the first round on Sunday. "I have a left thigh injury and, unfortunately, have to withdraw from this year's Madrid Open," said Williams. "It happened during my first round match. It started to get better, but most importantly right now, I just need some time to rest and recover. It's beyond words. It's so frustrating."However, the American insisted that she will try to defend her title at the Italian Open in Rome next week. "I am planning to play in Rome. Fortunately, I have a bye next week so will have an extra day of rest. For now, I will take it one day at a time and take advantage of some extra rest."Sharapova has been beaten by Williams in Madrid in the last two years, including in the 2013 final, and the Russian is now the favourite to clinch her first title in the Spanish capital as she edged a thrilling match against second seed Li 2-6, 7-6 (7/5), 6-3. "I will say the match was very close. I think it really could have gone her way today," admitted Sharapova."It was just a matter of a few points in the second set and in the third, although I was up a break throughout the third set, you know she's not going to let go. I didn't win the match until the last point was played." Li looked on course for the semi-finals when she broke to lead 4-3 in the second set. However, Sharapova broke back immediately and, despite needing four set points, finally forced the match into a deciding set when Li netted at 5-6 down in the tie-break. There were three breaks of serve to open the third set, but Sharapova took control when she finally consolidated the break at 3-1 and was gifted the final game when Li double faulted on match point. The four-time Grand Slam champion will face third seed Agnieszka Radwanska or French qualifier Caroline Garcia in the semi-finals. Also into Saturday's semis is fourth seed Simona Halep as she set up a meeting with Kvitova thanks to a 6-2, 6-2 thrashing of Serbia's Ana Ivanovic.Hsieh to become Taiwan's first world No 1: Hsieh Su-Wei will become Taiwan's first tennis world number one when she joins her partner Peng Shuai at the top of the doubles rankings, the Women's Tennis Association (WTA) said Friday. Hsieh and China's Peng, who are into the Madrid Open semi-finals, will be listed as joint world number ones in the new rankings released on Monday. "Reaching number one in the world is a great feeling," said Hsieh, 28. "We have been working really hard as a team. "I was very proud Peng reached number one earlier this year and now I am happy we can share it."Hsieh and Peng have won 11 WTA titles together and have never lost a final. They are the 10th doubles team to be listed as co-number ones. "It is a great accomplishment for Hsieh Su-Wei to join Peng Shuai as co-world number ones," said WTA chairman and CEO Stacey Allaster. "Not only are Hsieh and Peng a great doubles team, but they are an inspiration to the fans throughout the Asia-Pacific region." Hsieh and Peng, who reached the top doubles ranking in February, will face Spain's Garbine Muguruza and Carla Suarez Navarro in the Madrid semi-finals on Friday.Federer will play French Open: Roger Federer will take part in the French Open despite earlier suggesting he may take time out to be with wife Mirka, who gave birth to the couple's second set of twins this week. Federer's agent, Tony Godsick, told www.ATPworldtour.com that the Swiss intends to feature at the French Open, which starts at Roland Garros in Paris on May 25, where he would stretch his consecutive run of Grand Slam events to 58. "Roger plans on playing Roland Garros and he will make a decision at the last minute if he will play Rome.” (next week) depending on how everything is going with his family," said Godsick. Mirka Federer gave birth to sons Leo and Lenny on Tuesday. The couple already have twin girls, Myla Rose and Charlene Ri, who will be five in July. Federer, 32, has played in a record 57 consecutive Grand Slam tournaments, this past January eclipsing the mark previously set by Wayne Ferreira in 2003. He will be making his 16th straight appearance at the French Open, where he won the title in 2009 to complete a career Slam.