NEW YORK -- For more than a decade, Serena and Venus Williams have made the United States the dominant power when it comes to Grand Slam events.

Since Serena won the 1999 U.S. Open at 17, there have been 56 Grand Slam tournaments. A Williams sister has won exactly half, 23 titles, and the United States has won 27 Grand Slam championships. The next closest nation is Belgium with 11 titles.

Even with their recent success -- Serena is the world No. 1 and Venus beat 12th seed Kirsten Flipkens on Monday at the U.S. Open -- it is hard to ignore their age. When Serena's birthday comes around on Sept. 26, both will be at least 32.

But a new crop of American women is on the rise.

Meet 20-year-old Sloane Stephens and 23-year-old Jamie Hampton, Serena's two fellow Americans ranked in the WTA's Top 30.

Stephens was born in Plantation, Fla., in 1993 to Sybil Smith, a swimmer at Boston University who became the first African-American female to be named First Team All-American in Division I, and John Stephens, a Pro Bowl running back.

Stephens began playing professional events at age 14 in 2007 and by the spring of 2008, she played in WTA Tour events. In late 2009, she turned pro at age 16 and in 2011, shortly after her 18th birthday, Stephens made her Grand Slam debut at the French Open, losing in the first round.

Stephens jumped into the limelight at the 2011 U.S. Open when she reached the third round. After a second-round victory over No. 23 seed Shahar Pe'er, she fell to former world No. 1 Ana Ivanovic.

Stephens ended 2011 as the No. 97 ranked player in the world.

In 2012, Stephens kept the train moving, getting through all four Grand Slam first rounds. She went as far as the fourth-round in the French Open. At the U.S. Open, Stephens again lost to Ivanovic in the third round. At the end of the year, Stephens slid into the top-50, the only teenager to hold a spot.

Stephens erupted in 2013. At the Australian Open, as the No. 29 seed, she defeated Serena Williams in the quarterfinals before losing to eventual champion Victoria Azarenka in the semifinals. She followed with a fourth-round run at the French Open and a quarterfinals appearance at Wimbledon.

Stephens is the No. 15 seed at this year's U.S. Open. Although she nearly experienced a first-round exit Monday, as she knocked off Mandy Minella 4-6, 6-3, 7-6 (7-5), Stephens is ready to take on the role of up-and-coming American.

"It's exciting to play at a home slam," she said. "I think I have to take advantage of the opportunity that was given to me, and I thought I did that well today."

Five months ago, Stephens was a teenager. Many 20-year-old Americans are starting college classes this week. Stephens is playing in her third U.S. Open.

That is not all. She is playing in it as one of her country's newest celebrities.

"I think just the whole being here at the U.S. Open is a bit overwhelming," she said. "Literally everywhere you go every single person knows who you are, as opposed to when you're at the French Open or when you're at Wimbledon. It's OK, like, you're a tennis player. That's great. Here, every person knows who you are."

Stephens won her three-set match on Louis Armstrong Stadium, the Billie Jean King National Tennis Center's No. 2 court and former Center Court. As the match reached its climax, the American fan base unleashed "Sloane Stephens!" chants that rivaled the grounds' PA system.

"I think it's all positive," she said of the support. "I like being at home. It's definitely a completely different feeling than being at any other tournament for a slam. I think people, they really get behind you."

As for winning the third set, which she was down 4-2, Stephens is unsure what string she pulled to help. "I don't know. I think it was brain power. I'm not sure."

Shortly before Stephens' match, Jamie Hampton took to Court 17. Hampton's path to stardom ran a different route. She was born in Frankfurt, West Germany. in 1990 to a U.S. Army officer and a South Korean mother. As a child, her family relocated to Enterprise, Alabama, and later Auburn, Alabama.

She turned pro at age 19 in September 2009 and by mid-2010, she entered WTA events. Hampton made her Grand Slam debut at the 2010 U.S. Open, losing her first round match to number 22 seed Spaniard Maria Jose Martinez Sanchez in three sets.

In 2011 and 2012, Hampton found herself on the cusp. She was present at six Grand Slams in the two years, but she only reached the second round twice, at the 2012 Australian Open and 2012 Wimbledon. Neither affair saw her stick around for the third round. Hampton finished 2012 as the No. 71 player in the world.

In 2013, things clicked for Hampton. In her opening tournament of the season, the ASB Classic in Auckland, New Zealand, Hampton made a run to the semifinals before losing in two tiebreakers to Agnieszka Radwanska.

The following week, Hampton made her deepest run in a Grand Slam, going to the third round of the Australian Open. Number one seed Victoria Azarenka spoiled her Melbourne trip with a three-set win en route to her second consecutive Australian Open title.

Hampton reached another semifinal in May on clay in Brussels. One week later, she upset seventh-seeded Nadia Petrova in the third round of the French Open. Hampton's new longest Grand Slam run was halted in the fourth round by No. 18 seed Jelena Jankovic.

Hampton's career year hit a peak in the United Kingdom, where she won a grass tournament in Eastbourne in June. Along the way, Hampton knocked off top-ten players Radwanska and Caroline Wozniacki.

Hampton's Wimbledon was spoiled by a draw that set her up in the opening-round match against Stephens. She fell 6-3, 6-3 to her fellow American.

Hampton made another semifinal after the tournament and her current ranking of number 24 in the world is the highest she has achieved. As with Stephens, this year's U.S. Open is the first time Hampton has been seeded at a Grand Slam tournament.

On paper, Hampton looks a lot bolder than she did in previous years. She claims her ranking does not affect the way other players look at her.

"Everybody treats me the same and I'd like to keep it that way," she says.

Despite each having multiple trips to Flushing under their belt, Stephens and Hampton are experiencing different emotions and expectations at this year's event. But are the youngsters ready to step in?

"They're big shoes to fill, to be honest," Hampton says. "Those are two game-changers. Will we be like that? It's tough to say. I certainly hope so."

Hampton took the first step on Monday. She finally escaped the first round at a U.S. Open, defeating Spaniard Lara Arruabarrena 6-4, 6-2 on Court 17.

Stephens and Hampton will both play their second-round matches Wednesday. Stephens takes on Urszula Radwanska, and Hampton gets Kristina Mladenovic.

As luck would have it, the youngsters are slotted for a third-round meeting if both continue to win.

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Hampton does not like to talk about hypothetical matchups, but she could not shy away from commenting on potential Arthur Ashe Stadium drama.

"Playing the American is always a little bit tougher because we know them really well," Hampton said. "You know their coaches, you know their team and everything. It definitely makes things a little tougher. We've got to get there first. Either way, I think it will be good for American tennis."

If Hampton does make it to Ashe, her youthful taste in music will show. When asked what song she would choose to come out to on Ashe, she gave a stereotypical 23-year-old answer.

"Right now, I'm kind of into the dance, electronic music. I'd probably choose Avicii right now," she said.

Stephens holds the upper hand in the head-to-head series, 2-1. She won their only meeting on hard court, a 6-2, 6-4 first-round victory at Indian Wells in 2011.

In an interesting twist, all three American-seeded women are located in the same eighth of the draw. The winner of that potential third-round matchup would likely face Serena Williams in the fourth. If that is not enough, there is potential for the winner of that match to have a date with Venus Williams in the quarterfinals.

With seeds next to their name and flag and potential marquee matchups on the horizon, Sloane Stephens and Jamie Hampton are no longer just two Americans in the U.S. Open draw. They are the future and this fortnight, they enter the bright lights of New York City.

With the red, white and blue waving in the crowds of their stadium courts, Stephens and Hampton got a taste of their new stardom Monday.

"Today, I had 75 different coaches out there because people are screaming hit the ball; hit it to her forehand; serve to her backhand; come to the net. You're just like, oh, goodness. I mean, it's tricky, but I think most of the time it's all positive," Stephens said.

She and Hampton must get used to the noise. It is coming for them. The chatter will bring expectations, pressure and nerves.

Stephens and Hampton look poised to take it at the net. That is good news for American tennis fans.

-- Follow Jeffrey Eisenband on Twitter @JeffEisenband.

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