Andrew Johnson: From Jr. Davis Cup title to youngest ITF champ since Alcaraz

Johnson also admires Tien, seeing similarities between his game and the tennis that helped the 20-year-old reach his first Grand Slam quarterfinal this year at the Australian Open. A cerebral player, Johnson emphasizes placement over power, with a heavy-spin forehand and a flat backhand. Having worked with Romanian coach Vasile Beches since he was 4 years old, there is a distinct European influence in his game.

But the Southern California kid has enjoyed an American tennis upbringing, training at the Jack Kramer Club in his native Palos Verdes and the USTA Training Center - West in Carson, with occasional sessions at the USTA National Campus in Orlando, Fla.

Representing the United States at last November's Junior Davis Cup, Johnson posted a perfect 10-0 record (evenly split across singles and doubles) to help his home nation win its second straight and fifth overall title at the event. With the U.S. girls also winning the Junior Billie Jean King Cup crown in back-to-back years, it marked the first time any nation has swept the trophies at the world's premier 16-and-under team competitions in consecutive years.

"It was an amazing experience, and an amazing accomplishment. I'm very proud for myself and for America to win the title," Johnson reflected. "It was probably one of the most fun tournaments I've ever been at. Traveling with five other people, and the coaches, everyone there was just so fun."

Read more: U.S. teams complete historic sweep at Junior Davis Cup & BJK Cup

Now a high school sophomore, Johnson's tennis education started young. His mother, a former junior tournament player herself, introduced him to the sport—and to coach Beches—when he was 4. Two years later, he played his first tournament and reached the semis.

"That was pretty cool, and ever since then I just kept playing, kept loving it, loving the competition, loving the fight," he said. "I've always had passion for tennis, forever."

After successfully begging his mom to put him in that first tournament at the age of 6, he may have another family debate on his hands at 16. Still too young to officially speak with NCAA coaches, Johnson is not sure if he wants to attend college or turn pro.

"My parents do want me to get that education," he said. "But if I keep doing well in tennis, you just never know."