Serena Williams' coach expects big things from Stefanos Tsitsipas, and so should you

Stefanos Tsitsipas enters the Next Gen ATP Finals coming off his first career title. Julian Finney/Getty Images

This past September at the US Open, Stefanos Tsitsipas realized how popular he had become.

"I received a message recently from one woman who said because of me, 71 percent of the kids [in Greek] schools choose to play tennis," Tsitsipas told ESPN.com. "So I was like, 'OK, I feel pretty proud of myself.' I mean, no one played tennis before, and now it's 71 percent. Wow, so it must be pretty nuts when I get back there."

Ever since he arrived on the scene in 2016 as an 18-year-old, Tsitsipas has been blazing a trail for his country. While Eleni Daniilidou reached No 14 in the women's game in 2003, no Greek man had made the ATP Tour's top 100 until Tsitsipas cracked it in October 2017.

Tsitsipas began the year ranked 91, but he made major leaps, reaching the final in Barcelona and Toronto, where he fell to Rafael Nadal both times. Finally, in late October, Tsitsipas broke through, winning the Stockholm title and becoming the first Greek man to win an ATP Tour championship. Today, Tsitsipas is ranked a career high No. 15 and closing the door on the top 10. On Tuesday, he beat Jaume Munar in the opening match at the Next Gen ATP Finals.

"Hopefully many Greek players can achieve something like this," Tsitsipas told reporters in Stockholm. "I would be super happy to see them achieve something like this in the future, maybe even in the near future. Representing my country at such high-level tournaments, being the first Greek to crack the top 100 is very, very special for me."

His rise to the top has been swift -- but not surprising. Four years ago, Patrick Mouratoglou, Serena Williams' coach since 2012, first heard of Tsitsipas.

"I knew he was Greek, so I was particularly interested, so I checked on YouTube," Mouratoglou, whose father is Greek, told ESPN.com. "It was easy. I saw him at the Orange Bowl [in December 2014] and immediately was impressed. I called the agent and I said bring him to my academy for a week. I want to see him."

Tsitsipas has been at the Mouratoglou Tennis Academy ever since, with Mouratoglou working as a mentor alongside his own father and Tsitsipas' father, Apostolos. Tsitsipas' mother, Julia, was a former tennis player, and his grandfather won an Olympic gold medal in soccer for the Soviet Union in 1956.

Yes, his pedigree has him in good stead, but it was his attitude caught the eye of Mouratoglou.

"I saw a great competitor," Mouratoglou said. "I think this is the No. 1 quality in tennis. This and the physical ability. If you're a great athlete and a great competitor and you have the right mentality and are a hard worker, then you can go really long way. He is looking for the short ball, to come in and go to the net. You felt that he wanted the decision to be his, whether he would win or lose, and that's great. Afterward, when I saw him play matches, I saw he was an incredible competitor."

With his long hair and headband, Tsitsipas resembles Bjorn Borg. His big serve is backed up by superb groundstrokes, and his one-handed backhand is one of the best around. His willingness to come forward has served him superbly to this point. Although he can lose his temper at times, Tsitsipas generally has a calm presence and is a smart thinker on and off court.

"I don't see any limit for him," Mouratoglou said. "There are so many things he can do better and he is already 15 in the world. It's a good sign."

Mouratoglou has an added reason to hope Tsitsipas does well. Now 20, Tsitsipas is the leader of Team Mouratoglou, or Team M, the name given for a small group of players who are based at the academy. Each player receives specialist attention on the court, in the gym and through Mouratoglou's state-of-the-art medical setup.

American Cori Gauff, who won this year's junior French Open at the age of 14, and Chun Hsin Tseng of Taiwan, the boys No. 1, are both part of a small team behind Tsitsipas, as is Australian Alexei Popyrin, who is already inside the top 200.

"It's not bad to be the leader of something," Tsitsipas said. "I think kids at the academy will be motivated to see that and they'll want to join in."

But the overall objective is to win Grand Slams. "Our responsibility with any player is to bring them to their maximum," Mouratoglou said. "If they don't win a Grand Slam, for me, we will not have done the job completely properly; it's not satisfying. You can't always succeed, but it's not satisfying."

Tsitsipas believes he is destined for the top. "Things are very bright," he said. "There is a future for sure, and this is just the beginning, in my opinion. We can achieve much more than this.