1

Age: 19

Ranking: No. 24

2016 Highlights: The German won his first ATP title in St. Petersburg by beating both Tomas Berdych and Stan Wawrinka. He also notched his first Top 10 win ever over Roger Federer in Halle.

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2

Age: 21

Ranking: No. 45

2016 Highlights: The Brit reached his first major fourth round at the US Open with a gritty upset over John Isner in the third round. He also stepped up in Davis Cup play, winning both his singles rubbers in Great Britain's quarterfinal win over Serbia.

3

Age: 22

Ranking: No. 15

2016 Highlights: The Frenchman came seemingly out of nowhere to upset Rafael Nadal in a fifth-set tiebreak in the US Open fourth round. After that dream run, he proved he was no flash in the pan, winning his first career title in Metz.

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4

Age: 20

Ranking: No. 53

2016 Highlights: The steadily rising Russian broke through in 2016 to win his first title in Chengdu. He also appeared in his first Grand Slam main draw, qualifying and winning his first round in New York City.

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5

Age: 19

Ranking: No. 76

2016 Highlights: The American reached his first ATP final in Memphis and appeared in the quarterfinals of Acapulco and Atlanta to become the youngest player inside the Top 100. The former No. 1 junior also picked up the ATP Star of Tomorrow award.