Teenager Madison Keys shrugged off a leg injury to advance to her maiden Grand Slam semifinal, outlasting 18th seed Venus Williams 6-3, 4-6, 6-4 on Wednesday.
Keys was slowed by what appeared to be a groin or thigh injury during the second set, and required a medical timeout.
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But the 19-year-old dug deep, tallying 34 winners to Williams' 10, to earn her first win against the seven-time Grand Slam champion after two hours on court.
Keys also becomes the first American teenager since Serena Williams at the 2001 U.S. Open to reach a Grand Slam semifinal. Keys and Serena, it so happens, will meet in this year's semifinals.
"It's amazing, you just have to embrace the moment," Keys told reporters. "And I get to enjoy another moment next round."
Keys broke a deadlock in the seventh game of the opening set by launching three forehand winners on Williams' serve. She then held serve to go up 5-3 before breaking Williams again at love for first-set honors after 29 minutes of play.
The first-set loss was Williams' second at the Australian Open this year. But just as she had done against Camila Giorgi, Williams regained her composure in the second set.
Two double faults from Keys, who had just a 22 percent success rate on her second serve, handed Williams an early break. Keys, clearly rattled and out of sorts, dropped serve again as Williams claimed a double break for a commanding 4-1 lead.
Keys then called for the trainer before taking a medical timeout with what appeared to be an injury to her upper left leg. That brief moment off the court gave Keys the chance to regroup, and it paid instant dividends as she broke back at love following four consecutive unforced errors from Williams.
Williams responded by securing a break in the ninth game before serving out the set. She leveled the match with an ace.
Williams and Keys exchanged breaks at the start of the deciding set to be level at 3-3. The pair continued to go toe-to-toe, Keys broken in the seventh game only to break back immediately. Keys closed out the match by breaking Williams at love.
Williams told reporters after the match that her season has gotten off to a "great start" despite Wednesday's loss. "Hopefully I'll be able to keep this level up," she said, according to The Associated Press.
Keys told reporters after the match that the injury was to her left adductor; The Associated Press noted that she was forced to retire from a match at Wimbledon last year with the same injury.
"I think it's one of those things where all of us have dealt with injuries before," she said, per the AP. "I'm probably going to have tape on it, but I'm just going to do my absolute best and enjoy the moment."
Contributing: Tom Gatto