MELBOURNE, Australia — In a match that felt like a changing of the guard, Madison Keys, an unseeded teenager from the United States, defeated 34-year-old Venus Williams on Wednesday to reach the semifinals of the Australian Open.
Keys, playing in her first Grand Slam quarterfinal, had to fight against her nerves and a left leg injury that surfaced in the second set. But she found the strength and the big shots she required to finish off her 6-3, 4-6, 6-4 victory.
“I’m very happy I’m into the semifinals, but the moment is definitely sweeter being able to play Venus,” Keys said. “You just have to enjoy the moment, and I did enjoy it, and I get to enjoy another moment next round.”
Williams said: “I definitely didn’t serve as consistently as I wanted to, and I felt just not as aggressive off the ground as I would have liked. I think in this kind of match you have to be aggressive but I give a lot of credit to her. She was swinging freely and most of them went in for her so it’s great for her.”
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Still, Keys knows she will need to be near her best in order to have any reasonable chance of beating the other Williams sister, the one with 18 Grand Slam singles titles and an enduring grip on the No. 1 ranking. Beating Serena Williams is a daunting enough prospect without a leg injury. Good treatment is essential.
“I know; that’s where I’m heading next,” Keys said Wednesday.
A version of this article appears in print on January 28, 2015, on page B12 of the New York edition with the headline: A Resilient Keys Ousts Williams. Order Reprints| Today’s Paper|Subscribe
