Melbourne, Australia (Sports Network) - Sloane Stephens outlasted an injured Serena Williams in the Australian Open quarterfinals on Wednesday to set up a semifinal matchup with world No. 1 and defending champion Victoria Azarenka.
The 29th-seeded Stephens reached her first career major semifinal with a 3-6, 7-5, 6-4 victory over her American compatriot, while Azarenka rolled into the semis with a 7-5, 6-1 victory over two-time Grand Slam champion Svetlana Kuznetsova.
After Williams rolled through the first set by converting the lone break of the stanza, the players traded breaks in the second set to knot the score at 2-2. Stephens then broke the third-seeded former No. 1 two more times to jump ahead 5-3 at Melbourne Park's Rod Laver Arena.
Stephens had a chance to serve for the second set, but a double fault led to deuce and Williams took advantage to earn a break.
Williams, however, suffered back spasms during the game and went into the locker room to receive treatment.
"Everyone at this stage in the locker room has something wrong with them. It's no excuse," she said. "I went for this drop shot and it just locked up on me. I couldn't really rotate after that.
"It was a little painful, but it's OK."
When she returned to the court, Williams held serve at love to knot the set at 5-5 despite losing some velocity on her shots. Stephens then took advantage of her hobbled opponent to force a third set.
"She was serving at lower speeds, but her serve, she hits spots," said Stephens. "No matter how slow it's going, it's right on the line. It's still a really good serve even though it's much slower."
Neither player could break the other in the third set until Stephens hit a forehand into the net after a long volley to give Williams a 4-3 advantage.
But Stephens answered with a break on an unforced error by Williams on her ensuing serve and another shot into the net by Williams put the 19-year-old ahead, 5-4, with a chance to break for the match.
In the decisive game, Williams again struggled to get her shots over the net as an unforced error, her 48th of the match, by the five-time Aussie Open titlist resulted in Stephens snapping Williams' 20-match win streak.
"I don't know how many unforced errors I ended up hitting, but for sure more in one set than I probably did in the whole tournament," a distraught Williams said.
Stephens has now split two career matches against the 15-time major champion Williams, the reigning U.S. Open and Wimbledon champ who was seeking a third straight Grand Slam title. Williams won their first meeting in Brisbane just three weeks ago.
An elated Stephens pulled her phone out of her tennis bag and started checking for a text message from her mother.
"I was hoping she had texted me right away. I thought maybe she was texting me during the match," Stephens said. "I'm sure my grandparents are like freaking out.
"This is so crazy. Oh my goodness," Stephens said, wiping away tears in her post-match TV interview. "I think I'll put a poster of myself (up) now."
The first match of the day did not start in Azarenka's favor, as the Belarusian fell into an early 1-3 hole in the first set after Russia's Kuznetsova was finally able to take a 10-deuce game with her first break.
But Azarenka returned the favor with a break of her own while also holding serve on her next two attempts to knot the score at 4-4.
Each player held serve over the next two games until Azarenka earned her second break of the set and then fought through another tough point to take the 77-minute first set.
The second set started with three straight breaks before Azarenka finally held serve at love to jump on top 3-1.
The 23-year-old Azarenka then closed out her dominant second set with two more breaks to advance and keep her hopes of a repeat title alive.
Azarenka is now 4-4 lifetime against Kuznetsova, including 1-2 in Grand Slam play. The Belarusian star will now play in her second straight Aussie Open semi and the fifth major semifinal of her career.
Thursday's semis will pit the top-seeded Azarenka against the rising Stephens and second-seeded former Aussie Open champ Maria Sharapova versus sixth-seeded 2011 Aussie runner-up Li Na. The reigning French Open champion Sharapova lost to Azarenka in last year's finale in Melbourne, titled here in 2008, and was also an Aussie runner-up in 2007. Li was the French Open champ two years ago.