Take a glimpse into the bright future of American women's tennis

When it comes to American women's tennis, the question of "Who comes next?" after Serena Williams and Venus Williams has become more pressing as the era-dominating sisters move further into their 30s.

CoCo Vandeweghe, 25, Sloane Stephens, 24, and Madison Keys, 22, have made it into the conversation in recent years, but there is a younger wave of talent coming up behind them that fans of American tennis can be excited about.

Just look at the last two major tournaments. There hadn't been an all-American girls' final at a junior Grand Slam since 1992, but we saw it at both Wimbledon and the French Open this year. Whitney Osuigwe's French Open girls' title broke a 28-year U.S. drought in that event, and Claire Liu snapped a 25-year U.S. drought at Wimbledon. They had company deep into those draws, too, with the U.S. producing four girls' quarterfinalists at Roland Garros and five at Wimbledon.

In the past decade, the USTA and IMG Academy have taken a new approach that is starting to bear fruit. The national governing body of tennis and the elite Florida training center started identifying the most talented girls as young as 8 years old and implementing a long-range plan to develop their all-around games. The result: A strong group of 15- to 18-year-old players are primed to take up the mantle from the Williams sisters.

Here's a closer look at five potential stars, oldest to youngest, from the USTA and IMG pipeline:

Catherine "CiCi" Bellis

Hometown: San Francisco

Age (DOB): 18 (April 8, 1999)

Current ranking: Pro: 36

Career-high rankings: Junior: 1; Pro: 36

What makes her special: Bellis is the most accomplished of the group, having surged from outside the WTA top 200 at the start of 2016 into the top 40. She is currently one of only four teenagers in the top 100, and only three Americans not named Williams are ranked above her. Chris Evert predicted earlier this year that Bellis will break into the top 20 by the end of the year, and her recent straight-set wins over two-time Wimbledon champion Petra Kvitova and No. 8 Svetlana Kuznetsova showed that she is headed in the right direction. Her game-winning strength is her knack for reading opponents' serves and sending back lethal returns.

Notable achievements: Won three ITF tournaments and one WTA 125K event in 2016; two-time WTA semifinalist in 2017.

Quotable: "She is such a fighter. She sees obstacles as an opportunity and she embraces the challenge. More obstacles mean more opportunities to get better in CiCi's books." Anibal Aranda, USTA coach

Kayla Day

Hometown: Santa Barbara, California

Age (DOB): 17 (September 28, 1999)

Current rankings: Juniors: 7; Pro: 126

Career-high rankings: Juniors: 1; Pro: 122

What makes her special: Day knows when to attack and when to play defense with a natural instinct to vary her game depending on the situation and opponent. Over the past year, according to USTA coach Roger Anderson, she has increased her racket speed to produce better quality shots to match the big players of the game. She has a powerful forehand and the ability to be patient and focused during baseline rallies and knows how to finish off points at the net, making her a tough opponent.

Notable achievements: 2017 Wimbledon junior quarterfinalist; 2016 US Open junior champion; 2016 ITF Macon singles champion; 2016 Pan American ITF Championship junior singles and doubles champion.

Quotable: "Kayla is a physical player and knows how to mix her shots to rattle even the best athletes, and she has really good anticipation on court and is great at problem-solving. She is at a stage in her career where she believes she can beat the top 100 in the world, and that's helping her game a lot." -- Roger Anderson, USTA coach

Claire Liu

Hometown: Thousand Oaks, California

Age (DOB): 17 (May 25, 2000)

Current rankings: Juniors: No. 1; Pro: 293

Career-high rankings: Juniors: 1; Pro: 275

What makes her special: Liu savors the process of waking up every morning for practice, training and strength and conditioning sessions. She enjoys it so much that sometimes her coaches tell her to stay away as a form of punishment, according Rodney Marshall, her conditioning coach at the USTA facility in Carson, California. From a young age she's seen what it takes to be a professional by watching the likes of Sam Querrey, Sloane Stephens and Mardy Fish while they trained. Add in a stellar backhand and serve and her ability to get to the net, and it makes Liu a scary opponent.

Notable achievements: 2017 Wimbledon junior title; 2017 French Open junior runner-up; won two ITF tournaments in 2017; in 2015 became youngest player to win a pro tournament since Anna Kournikova (1996).

Quotable: "It's hard to beat her in singles because she is good at everything -- serving big, volleying and finishing off points on the net -- and it's great to play doubles with her because she will serve big and set up the point for me to finish off." -- Taylor Johnson, Liu's doubles partner

Ann Li

Hometown: King of Prussia, Pennsylvania

Age: 17 (June 26, 2000)

Current rankings: Juniors: 17; Pro: 918

Career-high rankings: Juniors: 14; Pro: 916

What makes her special: Ever since Li started playing tennis, her coach Jon Glover had a long-term goal for her to develop all aspects of her game. Now she can take control of the point coming off of her second serve, slice with precision and get her opponents to move from one end of the court to the other. Glover's goal paid off, because Li now possesses multiple weapons and unleashes them through the course of her matches.

Notable achievements: 2017 Wimbledon junior runner-up; 2017 ITF Evansville champion.

Quotable: "A few years ago when she plays top players, she would panic and it was hard for her to close out matches. Now, she has become confident having played against many top players and she has the confidence to finish off big matches." -- Jon Glover, USTA coach

Whitney Osuigwe

Hometown: Bradenton, Florida

Age (DOB): 15 (April 17, 2002)

Current rankings: Juniors: 2; Pro: 1,232

Career-high rankings: Juniors: 2; Pro: 1,099

What makes her special: Osuigwe is a shy 15-year-old off the court, but on it she is like a ferocious tiger, according to Margie Zesinger, her coach at IMG Academy. She is confident, smart and makes her opponent work for every point. Her goal for 2018 is to further the transition from junior tennis to the pro ranks (she will be allowed to participate in unlimited pro tournaments once she turns 16) and continue to improve her game.

Notable achievements: 2017 French Open girls' title; member of 2017 Junior Fed Cup team; went from No. 111 to No. 2 in junior rankings in six months.

Quotable: "Many players play it safe when they are down, but Whitney thrives off of the pressure. She knows how to play risky tennis in pressure situations." -- Margie Zesinger, IMG Academy coach