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Garbiñe Muguruza scored a surprise straight-set upset of favorite Serena Williams in the second round of the French Open on Wednesday.

Williams, the defending champion and winner of 17 Grand Slam singles titles, fell 6-2, 6-2 to a 20-year tennis player with Spanish citizenship who was born in Caracas to a Venezuelan mother and a Spanish father.

It is her earliest exit at a major tournament since falling in the first round at Roland Garros two years ago.

A short time earlier, older sister Venus was eliminated by Anna Schmiedlova of Slovakia 2-6, 6-3, 6-4.

The Williams siblings would have met in the third round had they both won.

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    "It was one of those days. You can't be on every day, and, gosh, I hate to be off during a Grand Slam," the top-seeded Serena said. "It happens, you know. It's not the end of the world. It is what it is."

    Serena struggled from the start against Muguruza, who is ranked No. 35 in the world, and finished the match with only eight winners and 29 unforced errors.

    "Just nothing really worked," Serena said. "I don't know anything that actually worked."

    Muguruza was playing at the French Open for only the second time in her career. She lost in the second round last year, but reached the fourth round at the Australian Open in January.

    “It’s amazing,” Muguruza said of by far the biggest win of her career. “I didn’t expect that. But I played very, very well. I am really happy. My plan was to be very aggressive and I think I did it very well. Now I have a big opportunity, and every match is very difficult here, but today is a great day.”

    The Williams sisters have lost on the same day at a major tournament only twice before, the last time during the fourth round of Wimbledon in 2011. The other time was at the French Open in 2008 in the third round.

    Since reaching the fourth round at Wimbledon in 2011, Venus has been eliminated in the first or second round at every Grand Slam tournament she has played except the 2013 Australian Open, where she reached the third round.

    Based on reporting by The Associated Press.

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