So here's the question 127 of the 128 women in the U.S. Open's main draw will ask themselves: How do you beat Serena Williams?
A solid return helps, of course. As can the occasional free point off a big serve. And an ability to hang in there at the baseline on extended groundstroke exchanges.
Still, women who have managed to pick up rare victories over Williams pointed not to any particular stroke but rather to a positive mindset as the key to defeating the woman seeded No. 1 and chasing a calendar-year Grand Slam at Flushing Meadows, where play begins Monday.
''If you want to beat her,'' two-time Wimbledon champion Petra Kvitova said, ''you have to believe that you can.''
As Alize Cornet, who is seeded 27th at the U.S. Open, summed it up: ''You need to go on court and `know' you can win.''
The No. 5-seeded Kvitova is responsible for one of Williams' two losses in 50 matches in 2015, on red clay at Madrid in early May. The other came against 12th-seeded Swiss teenager Belinda Bencic on a hard court at Toronto this month.
''If you see her on the other side of the net, you know you have to play great to beat her,'' Kvitova said. ''Even if she is not playing well, we've seen her come back. Opponents know it's not (over), even if you are leading.''
Eleven of Williams' 48 victories this season came despite dropping the opening set.
As for what general advice she would give someone facing Williams, Kvitova laughed and responded: ''I'm going to keep it to myself.''
Then Kvitova, who could meet Williams only in the U.S. Open final, offered this tidbit: ''Try to play aggressively against her serve.''
Williams' serve is as good as it gets in women's tennis. When it breaks down, though, that can provide an opening.
Against Bencic, for example, Williams put in only 50 percent of first serves and double-faulted 12 times.
''Obviously she wasn't serving as great as she normally does,'' acknowledged Bencic, who could face Williams in the U.S. Open quarterfinals.
Williams' self-assessment after losing in Toronto?
''I played like an amateur, to be honest,'' she said that day.
Clearly, it helps to have an off-target performance from Williams, who has been dealing with a problematic right elbow.
And yet, when the stage is biggest and spotlight the brightest - in other words, at Grand Slam tournaments, particularly in the latter rounds - Williams plays her best.
She has won the last four major championships overall, and the past three U.S. Opens.
''She might have a bit of a shock loss here and there,'' said Sam Stosur, the last woman to beat Williams at Flushing Meadows, in the 2011 final, ''but when she needs to turn it on, she can absolutely do that.''
If Kvitova focuses on her returns against Williams, Stosur points to her own serve.
''If I do A, B and C well, then I've got a chance,'' the 22nd-seeded Stosur said. ''I feel like she doesn't like handling my kick serve.''
What else helps?
''Some points in matches are bigger than others,'' Stosur said, ''and in those moments, you have to back yourself to go after it, because you know for sure that she will.''
Williams' most recent Grand Slam loss came in June 2014, against Cornet in Wimbledon's third round. This is what Cornet said afterward: ''When she plays someone who finds the right tactics, she looks a bit lost on the court. In my opinion, there are more and more players understanding how to play her.''
Williams is 28-0 at majors since. Reminded of that declaration, Cornet chuckled and said: ''I guess, maybe, I was wrong.''
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