-- MELBOURNE, Australia -- Victoria Azarenka's run as Australian Open champion ended in a yelling, screaming quarterfinal defeat to Agnieszka Radwanska on Wednesday, continuing the flow of stars tumbling out of the season's first major.
Fifth-seeded Radwanska stopped Azarenka's 18-match winning run at Melbourne Park and her own streak of three consecutive quarterfinal defeats at the Australian Open, winning 6-1, 5-7, 6-0 with a stunning display of versatility and court craft that shocked and confused the two-time champion.
The result means both defending champions were out in the quarterfinals -- Novak Djokovic lost in five sets to Stan Wawrinka on Tuesday night.
With the three biggest stars of the women's game falling one by one -- top-seeded Serena Williams, followed by Maria Sharapova and two-time Australian Open champion Victoria Azarenka -- the door has opened for a first-time winner at Melbourne Park.
Only fourth-seeded Li Na has won a Grand Slam before -- the 2011 French Open.
Li, a two-time finalist in Australia, will play 19-year-old Canadian Eugenie Bouchard in the other semifinal.
Radwanska played drop shots and slices from the baseline, forcing Azarenka to come forward and then lobbing or passing her. She hit touch volleys with calm precision, and instinctively anticipated Azarenka's shots.
She didn't fall into big-swinging rallies against the second-seeded Azarenka, either, continually mixing it up and saving the power for when she needed it.
"She was aggressive. She was making everything. She was guessing right," Azarenka said. "I was just playing a little bit too predictably.
"In the second set I managed to fight back. Third set, the first game was important. I let it go, like easily let it go. From there just couldn't get back to it."
Radwanska was also safe on her own serve, dropping just two games in the two-hour match while breaking Azarenka six times. She hadn't beaten Azarenka in their last seven matches, and had only won three of their previous 13.
"I said to myself one day I have to have one step forward and do the semifinal, and I'm so, so happy that I did it finally," Radwanska said of her first run to the semis of a major on hard courts. She reached the final at Wimbledon in 2012, becoming the first player from Poland to reach a major final in the Open Era, and the semifinals last year.
"I really had nothing to lose. She was defending the title, not me. I was really trying to play my best tennis, go for every shot I could," Radwanska said.
Azarenka went down in a flurry of unforced errors, making 47 in three sets as she tried to push Radwanska around.
She seemed to have momentum at the end of the second set, when she leveled after breaking in the last game. But she didn't carry it through, pushing a forehand fractionally too wide on the first point and unsuccessfully challenging the out call.
It was a sign of things to come. She won only 14 points in the third set, and was broken three times.
Azarenka was booed late in the match, when she smashed a ball into the back of the court after another frustrating error. She screamed loudly after losing big points to the incredibly consistent Radwanska, punched her thigh and her racket and even slapped the court. Nothing worked to change her fortunes.
"I'm not happy with what I did today, but on the court I felt like I could have played a lot better," Azarenka said. "I can't take away what she's done today. She played amazing."
The diminutive Cibulkova, among the shortest women on the WTA tour at 5-foot-3, pounded Halep from the back of the court to progress to her first Grand Slam semifinal since the 2009 French Open.
It was her second win in five major quarterfinals and served as a harsh lesson for Halep, who was appearing in her first.
"I'm not so tall, but I'm intense on the court," Cibulkova said, "and I'm powerful."
Halep only won 10 points in the second set as Cibulkova relentlessly attacked.
No. 20-seeded Cibulkova said her experience in the quarterfinals was the biggest factor against Halep, as "I was ready today and I knew what to expect ... I was perfect."
With such a golden opportunity for one of the four to now break through and capture a major, the deciding factor in the semifinals may be who can best handle the pressure.
Fifth-seeded Radwanska had never been beyond the quarters in Melbourne until she chipped, lobbed and sliced Azarenka off the court in a remarkable display of shot-making on Wednesday.
Cibulkova has made just one Grand Slam semifinal before, while Bouchard is a only playing her fourth major -- she didn't even make it out of qualifying at last year's Australian Open.
"Of course, a couple seeded (players) are out. Doesn't mean it's going to be easier and you have a title right away," Radwanska said. "It's a bit more pressure. This is the semifinal of a Grand Slam."
Radwanska should know. The draw opened up similarly at Wimbledon last year when Williams and Sharapova were upset early and Azarenka pulled out with an injury, leaving the Polish player as the highest remaining seed and the favorite to capture her first major.
Radwanska, however, crumpled in the semifinals against Sabine Lisicki, blowing a 3-0 lead in the third set. She said it's natural to feel nervous in these situations.
"I think in the beginning of the match it's always a little bit tough, especially it's the first semifinal," she said. "But hopefully after few games I'm going to be myself and play my best tennis."
Radwanska faces Cibulkova in the semis -- a player she's beaten four times in five matches, including a 6-0, 6-0 drubbing in the Sydney International final last year.
Cibulkova knows she doesn't have a great record against Radwanska, but she takes inspiration from Wawrinka's upset of four-time men's champion Djokovic in the quarterfinals after 14 consecutive losses to the Serb.
"You just want to prove it to yourself that you can do it, and that's what (Wawrinka) did," Cibulkova said.
Li has the most experience of any of the semifinalists playing in the latter stages of slams, but she's also been susceptible to buckling under pressure.
Li was up a set in the finals here against Kim Clijsters in 2011 and Azarenka in 2013, only to falter both times. She also nervously wasted four match points in a fourth-round loss to Clijsters in 2012, breaking down in tears afterward.
The Chinese star was almost out of this year's tournament, as well, saving a match point against Lucie Safarova in the third round. Since then, however, she's appeared more focused on court, dropping just six games in her last two matches.
The wild card is Bouchard. Li, who will be 32 next month, is 12 years older than the Canadian and has won their only previous meeting, but Bouchard is a rising talent with nothing to lose. She likes her chances in a tournament as topsy-turvy as this one.
"I think some players can still lose on any given day and it still makes it extremely interesting," she said. "I'm feeling confident and just excited to play."
The Associated Press contributed to this report.