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Associated Press
Novak Djokovic of Serbia takes a drink during a break as he plays Lleyton Hewitt of Australia during their fourth round match at the Australian Open tennis championship, in Melbourne, Australia, Monday, Jan. 23, 2012. (AP Photo/Aaron Favila)

By JOHN PYE

Associated Press

MELBOURNE, Australia — Third-seeded Victoria Azarenka reached the Australian Open semifinals when she held her nerve despite trouble with her serve in a 6-7 (0), 6-0, 6-2 win over No. 8 Agnieszka Radwanska on Tuesday.

It was only her second win in six Grand Slam quarterfinals. She's never gone further than the semis, and next meets the winner of Tuesday's later match between No. 1-ranked Caroline Wozniacki and defending champion Kim Clijsters.

The 22-year-old Belarusian extended her winning streak this season to 10 matches, including a title at Sydney where she beat Radwanska in the semifinals.

"I'm really glad I could stay tough and finish the match," she said. "I'm just really happy to be in the semifinals to give it all out there."

Azarenka lost just 12 games in the first four rounds. But she had six double faults and made 38 unforced errors during her 2-hour match against Radwanska.

The first set featured eight service breaks, and there were 15 overall in the match. Azarenka's double fault helped give Radwanska a 6-0 lead in the tiebreaker, followed by a wild errant backhand by Azarenka on set point.

But Azarenka, who can attain the No. 1 ranking by the end of the tournament, won the next seven games to move closer to the victory as the temperature increased to 93 at Rod Laver Arena.

Five-time champion Serena Williams is already out of the tournament. Her 17-match winning streak at the Australian Open ended in a 6-2, 6-3 loss to No. 56-ranked Ekaterina Makarova.

The margin equaled the biggest Grand Slam defeat of Williams' 17-year career.

Makarova will face three-time major winner Maria Sharapova in an all-Russian quarterfinal.

Sharapova rallied past Sabine Lisicki 3-6, 6-2, 6-3 before defending men's champion Novak Djokovic fended off a resurgent Lleyton Hewitt in a dramatic last match of the day, winning 6-1, 6-3, 4-6, 6-3.

Next up for Djokovic is fifth-seeded David Ferrer of Spain, who had a surprisingly easy 6-4, 6-4, 6-1 win over Richard Gasquet.

Wimbledon champion Petra Kvitova opened Monday's play with a 6-2, 7-6 (2) win over former top-ranked Ana Ivanovic. She'll next play Sara Errani of Italy, who beat 2010 semifinalist Zheng Jie 6-2, 6-1.

Two-time finalist Andy Murray advanced when Mikhail Kukushkin of Kazakhstan retired after 49 minutes with a left hip injury while trailing 6-1, 6-1, 1-0. After knocking out the first player from Kazakhstan to reach the fourth round of a Grand Slam, Murray's next opponent will be another history-maker.

Kei Nishikori beat sixth-seeded Jo-Wilfried Tsonga 2-6, 6-2, 6-1, 3-6, 6-3 to become the first Japanese man to reach the quarterfinals of the Australian Open since the Open era began in 1968.

No. 2 Rafael Nadal and No. 3 Roger Federer are back in action Tuesday, hoping to set up a semifinal meeting. Federer plays former U.S. Open champion Juan Martin del Potro while Nadal faces Tomas Berdych.