Sloane Stephens, 19, advances

PARIS -- Well, that's settled: 19-year-old Sloane Stephens is bumping herself up to first class for the flight home from the French Open, whenever that might be.

That extra-comfy trip back to Coral Springs, Fla., is among the benefits the American is looking forward to after reaching the fourth round at Roland Garros by beating Mathilde Johansson of France 6-3, 6-2 Friday.

Another perk?

"Now I'm going to have more Twitter followers," explained the bubbly Stephens, the only teenager left at the fourth, and most successful, Grand Slam tournament of her nascent career. "That's good. I'm excited. I mean, it's always good to be noticed and recognized."

She'd better get used to both.

With her ever-improving game, athletic parents -- her late father, John Stephens, was the 1988 NFL Offensive Rookie of the Year with the New England Patriots; her mother, Sybil Smith, was Boston University's first All-American in women's swimming -- and infectious personality, Stephens might just be the next big thing in U.S. tennis.

Asked what her daughter's greatest strength is, Smith said: "Probably her mental fortitude. She's a really happy-go-lucky kind of person, and she doesn't let things get her down. She's resilient. She's incredibly resilient."

That attribute helped last month, when Stephens was in Europe and struggling a bit.

Something had to change, so she cut out candy and her two-a-day orange soda habit -- "I was like, 'Whoa, that's a lot of sugar,' " she said -- and made a key telephone call, asking Smith and an aunt to travel overseas and be with her.

"The only way to go was up. So my mom came, and my aunt came, and that helped me a lot, because I don't know what was going on. ... I was having brain farts and things weren't going my way," Stephens said. "I was being 19, and I think now I am being 29. So I think my mom and aunt definitely helped me through the last couple of weeks. I'm very grateful for that."

Second-seeded Maria Sharapova also advanced Friday, while Ana Ivanovic lost in three sets.

Sharapova defeated Ayumi Morita of Japan 6-1, 6-1 in a match postponed a day by the marathon contest between American John Isner and Frenchman Paul-Henri Mathieu.

Sharapova has won three major titles in her career, but she still needs to win at Roland Garros to complete a career Grand Slam.

"I really wanted to try to get her on the move. I thought I played well, aggressive, moved in when I had to," Sharapova said. "With every round I'm going to be playing tougher opponents, and that's when you really want to kind of step it up and raise your level. That's what I'll try to do in the next round."

Ivanovic fell to Sara Errani of Italy 1-6, 7-5, 6-3.

Stephens ended a three-match losing streak by qualifying for the Italian Open, where she reached the second round, then got to her first WTA semifinal at Strasbourg.

And now there's a breakout performance at Roland Garros, where the toughest test yet will come when Stephens faces reigning U.S. Open champion and 2010 French Open runner-up Samantha Stosur with a quarterfinal berth at stake.

"My goal coming into the French Open was just (to) play hard. I mean, there's nothing else you can do. Play hard, fight hard, you know, run every ball down. Winning or losing, really, it didn't matter," the 70th-ranked Stephens said. "I was kind of like, 'I know, if I just do the right things, that good things will happen.' "

She gave Johansson all sorts of trouble in the French Open's main stadium, silencing the partisan crowd and putting together a 26-10 edge in winners.

Stephens also broke Johansson in seven of her nine service games.

"She's so powerful. She can hit winners on any type of ball," the 93rd-ranked Johansson said.

"I didn't really know what to do to fight back. She didn't give me any easy points," Johansson added. "I had to fight for each point, each game, and, frankly, I think she was a lot tougher than I was. ... She was quite impressive."

That's a good word to describe Stephens in front of a microphone, too.

After her second-round victory in Paris, Stephens joked about wanting to keep winning because Smith "is spoiled rotten, so she's going to want to fly first class home or something."

When she guaranteed herself about $100,000 in prize money by reaching the fourth round, Stephens said she'll "definitely, definitely" be purchasing a fancier airplane ticket for herself.

As for whether her mom and aunt will be traveling that way, too, Stephens replied with a wink: "I don't know what they're going to be doing, but I know where I'm going to be."

The 13th-seeded Ivanovic, a former top-ranked player who won the French Open title in 2008, committed 37 of her 40 unforced errors in the final two sets. Errani had only 18.

"In the third set I was creating a lot of opportunities and missing a lot of easy, easy finishing balls," Ivanovic said. "That's something that I'm not really happy about."

Also Friday, third-seeded Agnieszka Radwanska was routed by 2009 champion Svetlana Kuznetsova 6-1, 6-2, two days after eliminating Venus Williams.

Radwanska didn't look anything like the player who overwhelmed seven-time Grand Slam champion Williams in straight sets.

"She was just playing very aggressive on both sides," Radwanska said of Kuznetsova. "She just had (an) answer for everything I was trying to do."

Radwanska has been having a stellar year on tour, winning three titles and moving up to a career-high No. 3 ranking last month. But she is the only player in the top 10 that has never reached a Grand Slam semifinal.

Radwanska dropped to 3-10 against the Russian, including her only two losses in tournament finals.

"It's always disappointing when losing in the first week of a Grand Slam, that's for sure," Radwanska said. "Today I didn't play bad, she was just playing unbelievable."

Before Friday's match, Radwanska had been 38-7 in 2012, with six of those losses coming against top-ranked Victoria Azarenka.

Kuznetsova, who also won the U.S. Open in 2004, has struggled since winning the title at Roland Garros three years ago, only reaching one Grand Slam quarterfinal.

Information from The Associated Press was used in this report.