Sloane Stephens raised her eyebrows and with a sly smile didn't hesitate in answering the question of whether this American teenager is tennis' next superstar.

"She is," Stephens said.

Bubbly and confident at the same time, the 19-year-old plays the part of the youngest woman ranked in the top 50 in the world.

Wins like Tuesday's are becoming routine. Stephens defeated 22nd-seeded Francesca Schiavone in the first round of the U.S. Open — technically an upset since the American is ranked 44th, a career best.

Then again, Stephens has advanced to at least the third round at three of her last four Grand Slam events. She won 6-3, 6-4 against the 2010 French Open champion on Tuesday.

"I don't have a crystal ball to see the future, but I can say that she's an athlete who has every possibility to produce some great tennis," Schiavone said. "It's difficult to say, 'So-and-so's going to be No. 1.' ... But first of all, she's athletic. She has long legs. She did some great sprints today. And she can change speeds, change the height of her shots. That's important."

Her successes assure Stephens that she doesn't need to do anything out of the ordinary to beat players like the 32-year-old Schiavone.

"I did everything that my coach asked me to do," Stephens said. "I just really stayed within myself and tried to do my best. For me, that's a big step. If you do everything you want to do in your match, if you accomplish all your goals for today, which I did, I'm pleased, very pleased with myself. That's something that gives you confidence, and that takes you far."

Stephens next faces 141st-ranked Tatjana Malek.

Schiavone, whose ranking has slipped to 26th from a career-best No. 4 in early 2011, acknowledged, "It wasn't an easy year for me."

"It was an even match, 50-50," she said. "So whoever is better or does a little more on the important points will win. She had that little extra today."

At 3-3 in the second set, Stephens broke Schiavone at love, the game ending on a double-fault. The Italian had seven of those in the match — five in her first service game.

Stephens had double match point at 5-3 against Schiavone's serve but couldn't convert. Trying to serve out the match, she fought off a break point then clinched the victory with a forehand winner down the line.

Stephens was thrilled her grandparents were in the stands — and she figured she had better close the match out in straight sets for them.

"My grandma, she gets so nervous," Stephens said. "Poor thing, she has heart problems. 'I hope I don't go to a third set because she's going to be freaking out.'"


AP Tennis Writer Howard Fendrich contributed to this report.


Follow Rachel Cohen at https://twitter.com/rachelcohenap.