INDIAN WELLS (California) (AFP) Second-seeded Caroline Wozniacki saw off the tenacious challenge of Zheng Jie Wednesday to book a semi-final showdown with good friend Agnieszka Radwanska at the BNP Paribas Open. Denmarks Wozniacki stepped it up in the third set to beat Zheng 6-4, 4-6, 6-1, claiming her first victory over the Chinese player in three attempts. Radwanska, the fifth seed from Poland defeated fourth-seeded Russian Elena Dementieva 6-4, 6-3, denying Dementieva a shot at a third title of the season after her victories in Sydney and the Paris Indoors. Wozniacki, whose parents are Polish, is a close friend of Radwanska. She said the two talk make-up and fashion and boys when they go out to dinner together, but will keep it businesslike on the court. You have to do that, said the 19-year-old who was last years US Open runner-up. Its just important to stay focused and dont think about whos on the other side. Wozniacki was pleased to get past Zheng, who took the second set with a more aggressive game but admitted she tired in the third. Both of us played really aggressively and were trying to make the other one run, because the one that opened up the point won the point most of the time, said Wozniacki, who twice broke Zheng in the second set but each time immediately gave the break back. Zheng took the set by breaking to love in the final game to extend the match. Sometimes even I thought that she was already far from the court, and somehow she made the angles still on the court, Wozniacki said. I mean, she played really well. She played aggressively, really flat, and we had many long rallies. Zheng said she sensed a new authority in Wozniacki, who she last played in Toronto last year. Right now she has a lot of confidence. I can feel she changed a lot on court, Zheng said. Radwanska closed out Dementieva with a flourish, serving a love game to reach the semi-finals at Indian Wells for the first time after quarter-final defeats the past two years. She has reached her second semi-final of the season without dropping a set in four matches. This year its already my second semi-final, so I think Im doing good, said the world number eight, who had surgery on the middle finger of her right hand after the season-ending Tour Championships last year. Dementieva was disappointed with a sluggish performance. I was so slow, Dementieva said. I was reaching for the ball instead of going forward and attacking her second serve. She slowed down the game a lot and mixed it up a lot. You have to be very aggressive. You have to step forward. You have to create something. I was way too slow. The remaining two quarter-finals will be played on Thursday, when sixth-seeded Serbian Jelena Jankovic takes on Russian Alisa Kleybanova and eighth-seeded Australian Samantha Stosur was scheduled to take on Spains Maria Jose Martinez Sanchez. Sharapova, Safina, Davydenko out of Miami Three-time Grand Slam champion Maria Sharapova will miss the Sony Ericsson Open, as will womens world number two Dinara Safina and 2008 mens champion Nikolay Davydenko, organizers said Wednesday. The Miami tournament is the second of prestigious back-to-back hardcourt tournaments in the United States, coming immediately after this weeks event at Indian Wells, California. Sharapova, who won the WTA title in Memphis in February, had been slated to play in Miami for the first time since 2007. But an MRI exam on the sore right elbow that hindered her as she made a third-round exit in Indian Wells showed a bone bruise that is likely to sideline the Russian for three to six weeks. Safina, a three-time Grand Slam finalist, remains sidelined by the back injury that forced her out of the Australian Open. Davydenko is out with a broken left wrist. He had played one match at Indian Wells and then pulled out after an MRI revealed the wrist he injured in Rotterdam last month was, in fact, fractured.