Who CAN Beat Serena?

For Serena Williams to lose her bid for the calendar-year Grand Slam, another player would have to step up and beat her, something that hasn't happened at a major in more than 14 months. While there will be 127 potential candidates for the role of vanquisher, there are few obvious choices. Serena has no rival—no Nadal to her Federer—nor has any one colleague played the burr in her saddle and vexed her. Still, before the making of the U.S. Open draw, here are five potential spoilers.

ANNA ITAINTOVATILLITSOVA

If you've never heard of her, it's for good reason. She doesn't exist. Still, the point is this: When Serena loses at majors, it tends to be against one of the WTA's lesser lights in the early rounds, when Serena's focus can waver and she has little knowledge of the opponent. Once Serena makes it to the second week and "locks in" (her term), you can all but hand her the trophy.

BELINDA BENCIC

The 18-year-old Swiss threw Serena a surprise defeat earlier this month in Toronto. Even if Bencic isn't likely to beat Serena again, she represents the type of player who can threaten her: a future star naive enough to swing away with nothing-to-lose abandon but seasoned and confident enough to know how to close.

ALIZÉ CORNET

Known among peers as the WTA's reigning drama queen, Cornet was remarkably unflappable when she beat Serena three times in 2014, including a takedown in the third round at Wimbledon. Acknowledging that she could not overpower Serena, Cornet outprecised her instead, and she didn't retreat when the match tightened.

VENUS WILLIAMS

There would be something of a Shakespearean dimension to Big Sister ruining Little Sister's run at history. Serena has beaten Venus in six of their last seven matches, but Venus has won eight of their 17 matches on hard courts. More important, the intrafamily dynamic is so strange and awkward that no result between the two is surprising.

MARIA SHARAPOVA OR VICTORIA AZARENKA

It sounds like a joke, given that Serena owns—and we mean owns—these alleged rivals, having prevailed in 18 of 20 matches against Sharapova (below) and 17 of 20 against Azarenka. But going strictly by the laws of probability, Serena should lose a match to one of them eventually. In theory.

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WARREN TODA/EPA (BENCIC)

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DAVE WINTER/ICON SPORT (CORNET)

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PAVEL GOLOVKIN/AP (V. WILLIAMS)

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CLIVE BRUNSKILL/GETTY IMAGES (SHARAPOVA)

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BOB MARTIN/AELTC (AZARENKA)