PARIS (AP) - If there truly is a secret to the success Sloane Stephens enjoys at Grand Slam tournaments, she isn't willing to share it.
After beating No. 22 Ekaterina Makarova of Russia 6-3, 6-4 to reach the fourth round at the French Open for the third year in a row, the 15th-seeded Stephens insisted Saturday that even she can't quite put a finger on why her results are so much better at tennis' four most important events than anywhere else.
What is different about the Slams?
''Nothing. I don't know. I don't know. I'm not sure. Honestly, if I had the answer and I knew,'' Stephens said, pivoting in her news conference chair and holding her arms out wide, ''I would tell you guys. I'd be like, `Oh, yeah!' But I can't even think of anything. Like, I don't know.''
Over the last two seasons, the American is 21-5 (an .808 winning percentage) in Grand Slam matches, but only 32-29 (.525) at run-of-the-mill tournaments.
She's made it to the second week at each of the past six majors, a run that began with a semifinal appearance at the 2013 Australian Open and stands as the longest active streak among women.
''I just peak at four tournaments a year,'' Stephens said. ''Every other tournament, I guess, just get me ready for these.''
The 21-year-old Stephens, who is based in Florida, is the last U.S. woman left of the 14 who were in the draw at Roland Garros.
There's also only one American man left, No. 10 John Isner, because the other two who were around lost Saturday: Jack Sock and Donald Young. Isner will play No. 6 Tomas Berdych of the Czech Republic on Sunday with a chance to give the United States its first man in the French Open quarterfinals since Andre Agassi in 2003.
Stephens will wait until Monday to take on No. 4 Simona Halep of Romania, with the winner earning her quarterfinal debut in Paris. Thanks to early losses by No. 1 Serena Williams, No. 2 Li Na, and No. 3 Agnieszka Radwanska, Halep is the highest-seeded woman remaining.
''That's a surprise for everyone,'' said Halep, who is reading Harry Potter books to try to improve her English.
If Stephens has trouble week-in, week-out on tour - she's never won a WTA title and made it as far as the quarterfinals anywhere only once, in 2014 at Indian Wells, California - Halep is still waiting for a real Grand Slam breakthrough.
''For me, the Grand Slam, it's different,'' Halep said, ''because I feel more pressure here.''
Her 1-2 head-to-head record against Stephens includes a win in their only previous meeting on clay, and a 6-1, 6-1 loss in their only past match at a major, in the first round of the 2013 Australian Open.
Halep finally got to the fourth round at a Grand Slam at the U.S. Open in September, then surpassed that by getting to the quarterfinals of this year's Australian Open.
But Halep has surged up the rankings since being 47th at the end of 2012 by winning six titles last season, then adding another in 2014, when she also was the runner-up on clay at Madrid three weeks ago and was a semifinalist at Indian Wells.
''She's played really, really well, like, in the smaller tournaments, like I haven't done, and she has a lot of experience with that,'' Stephens said. ''I have a lot of experience here.''
Copyright 2014 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.