MELBOURNE — Serena Williams’s dominating run at the majors is over, and American teenager Sloane Stephens is headed to the semifinals of the Australian Open.
Williams injured her back in the second set, hampering her serve, and the 19-year-old Stephens kept her composure in a 3-6, 7-5, 6-4 victory on Wednesday.
It was the first loss since Aug. 17 for the 15-time Grand Slam winner, ending a run of 20 consecutive wins. She hadn’t lost a match at a Grand Slam tournament since the French Open, where the first-round exit sparked a resurgence in the second half of 2012 that included titles at Wimbledon, the London Olympics, the US Open, and the WTA Championship.
At the end, Williams had a swollen ankle and a spasming back, part of a two-week period that she described as the worst she had experienced at a grand slam.
“I'm almost relieved that it's over because there's only so much I felt I could do,” she said. “Oh my gosh, it's been a little difficult. I've been thrown a lot of balls these two weeks.
“I've had a tough two weeks between the ankle, which is like this big every day,” she added, gesturing with her hands. "And my back, which started hurting. A lot of stuff."
Stephens, after winning her first Grand Slam quarterfinal, next plays defending champion Victoria Azarenka.
With her most famous fan sitting in the crowd wearing a shirt reminding her to keep calm, Azarenka overcame some early jitters to beat Svetlana Kuznetsova, 7-5, 6-1.
After dropping serve in a long fourth game that went to deuce 10 times, Azarenka recovered to dominate the rest of the match against Kuznetsova, a two-time major winner who was floating dangerously in the draw with a No. 75 ranking as she recovers from a knee injury.
Azarenka’s American rapper friend, Redfoo, returned from a concert in Malaysia to attend Wednesday’s quarterfinal.
Wearing a red sleeveless T-shirt, that read, ‘‘Keep Calm and Bring Out the Bottles,’ — which is the name of his next single — Redfoo stood, clapped and yelled, ‘‘Come on, Vika!’’ during the tight first set.
Asked if it helped to have her No. 1 fan wearing a keep calm logo, Azareka said, ‘‘I was looking more at the part that says, ‘Bring out the bottles.’ ’’
Of her game, she added, ‘‘I'm just glad I could produce my good tennis when it was needed.’’
In the men’s quarterfinals, 17-time major winner Roger Federer played No. 7 Jo-Wilfried Tsonga in a night match and US Open champion Andy Murray was to meet Jeremy Chardy of France.
Novak Djokovic made it through to the semifinals with his 6-1, 4-6, 6-1, 6-4 win over fifth-seeded Tomas Berdych on Tuesday night.
The 2-hour-31-minute victory took half the time of his five-set win two nights previously against Stanislas Wawrinka.
In the early hours Monday morning, Djokovic ripped off his sweat-drenched shirt and flexed his muscles, mimicking his victory celebration after the 5:53 victory over Rafael Nadal in the 2012 Australian final.
That was acceptable at the time to the Rod Laver Arena crowd, which was still abuzz at 1:40 a.m. following five sets of high-level tennis.
After the Berdych match, however, Djokovic realized there was no need to raise the roof. He calmly pumped his fist once and walked to the net; he later joked about the ice baths he’d taken between matches on the advice of local hero Lleyton Hewitt.
‘‘It was a great performance. I was hoping to have a shorter match . . . just not to go over five hours,’’ Djokovic said.
In the semifinals, Djokovic will meet No. 4-seeded David Ferrer, who survived a quarterfinal battle with fellow Spaniard Nicolas Almagro.
Almagro had three chances to serve for the match, but Ferrer broke back each time and went on to win, 4-6, 4-6, 7-5, 7-6 (7-4), 6-2.
Ferrer has never gone farther than a major semifinal. There are only three men left in the draw who have won Grand Slam titles — Djokovic has won five, including the last two in Australia.