MELBOURNE, Australia — Kim Clijsters is moving on, and Caroline Wozniacki is moving out of the top spot.
Clijsters continued her Australian Open title defense with a 6-3, 7-6 (4) quarterfinal win that will cost Wozniacki the No. 1 ranking.
The four-time major winner next plays third-seeded Victoria Azarenka, who had a 6-7 (0), 6-0, 6-2 win over No. 8 Agnieszka Radwanska earlier Tuesday to move into the semis of a Grand Slam for the second time.
Azarenka is one of three players who can pass Wozniacki, who needed to reach the semifinals to retain the top ranking.
The 21-year-old Danish player has finished the last two seasons at No. 1 but has never won a major, prompting criticism of how the rankings system works.
Clijsters has slipped to No. 14 since beating Li Na in the last Australian final, losing in the second round at the French Open and then missing the next two majors due to injuries.
She also had a roller-coaster ride into the Australian Open semis for the seventh time after spraining her ankle and having to save four match points in a fourth-round win over Li.
Clijsters and Wozniacki both started nervously, with three service breaks to start the match. But the 28-year-old Belgian dictated play from her first hold in the fourth game until she was serving for the match at 5-3 in the second.
She had the rally on her racket at 30-30 but let her guard down and allowed Wozniacki back into the match. Wozniacki won the next two points to break Clijsters, and then held to get it back on level terms.
Clijsters had never lost any of her eight previous tiebreakers at Melbourne Park, and she hit a backhand down the line to take a 5-4 lead. She set up double match point with a cross-court forehand winner and sealed it with a volley.
"It definitely didn't feel like being up a set and 5-2," Clijsters said. "I had to work really hard for it. Caroline is a great fighter.
"I was happy to get through, and not in a three-setter because it's so hot," she said.
The crowd at Rod Laver Arena was solidly behind Clijsters from the start, shouting "C'mon Kimmie" in between nearly every point and cheering when Wozniacki missed a shot.
One group of Belgian fans had painted their faces in the red, yellow and black colors of the flag. They stood and chanted for Clijsters when she broke Wozniacki to win the first set.
Four-time Australian Open champion Roger Federer had the next scheduled match on Rod Laver against U.S. Open champion Juan Martin del Potro. No. 2-ranked Rafael Nadal played Tomas Berdych in a night match.
Azarenka opened the action on Rod Laver in a match that contained 15 breaks of serve, including eight in the first set.
After being comprehensively outplayed in the opening tiebreaker, Azarenka won seven straight games to move closer to the victory as the temperature increased to 93.
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," said Azarenka, who served six double-faults and had 38 unforced errors. "I'm just really happy to be in the semifinals to give it all out there."
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.
With Hewitt's loss, Australia's chances of celebrating a home singles winner were over. American hopes had already evaporated with the defeat of Williams — her first in Melbourne since 2008 and earliest since 2006.
"I can't even describe how I served, to be honest," said Williams, who finished with seven double-faults, including four in one game in the second set. "My lefty serve is actually better than that. Maybe I should have started serving lefty."
Williams tried not to blame her left ankle injury from a tuneup tournament in Brisbane two weeks ago. But she didn't move well and seemed to have particular difficulty running to her left. She said if it hadn't been a Grand Slam, she wouldn't have played at all.
"Usually I play myself into the tournament," Williams said. "But I don't have a huge problem with an injury. So this is a completely different situation. Usually it's easier for me to play myself in because I'm usually physically OK."
Wimbledon champion Petra Kvitova had a 6-2, 7-6 (2) win over former top-ranked Ana Ivanovic on Monday and will next play Sara Errani of Italy, who beat 2010 semifinalist Zheng Jie 6-2, 6-1.
Djokovic had won 23 straight sets at Melbourne Park before he suddenly wobbled against Hewitt, a two-time Grand Slam champion who has slipped to No. 181 in the rankings after a series of injuries.
Hewitt, a wild-card entry in his 16th straight Australian Open, rallied from 3-0 down in the third set in front of a raucous home crowd to force a fourth set, but Djokovic gathered his composure.
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.
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.