Sinner, 22, has dominating talent and has already beaten many of tennis’s top players.It wasn’t long after Darren Cahill began helping to coach Jannik Sinner last year that he started pulling out videos for his young charge to watch.Cahill knew the extraordinary speed that Sinner already possessed off both wings. He was aware of Sinner’s ability to maneuver around the court at speed and of his work ethic. But Cahill felt that Sinner could benefit by studying the ground strokes, particularly the backhand, of a former Cahill pupil, the eight-time major champion Andre Agassi.“Jannik’s lanky and tall, so he’s got a big wingspan and can generate a ton of power,” Cahill said by phone of Sinner, who is about 6-foot-2. “Andre was revolutionary in the way that he hit the ball back in the day, especially on the backhand. There’s so much to learn from a lot of the older-generation players. Because of the equipment and technology that they had, they really simplified a lot of things, especially the great players.”Sinner, 22, has been one of the most talked-about players since he won the Next Gen ATP Finals in 2019. He was also named the ATP’s Newcomer of the Year that season.“He’s got some of the hardest ground strokes I’ve probably ever had to deal with,” said Alex de Minaur, who lost to Sinner in the final in Toronto in August.“A couple of years ago, in a lot of matches, he was breaking down physically,” said Darren Cahill, left. “He was a late developer, so he just needed to make sure that his body could deal with the rigors of playing at this level week in and week out.”Clive Brunskill/Getty ImagesBut is Sinner a genuine threat to do damage, or even win, the ATP Finals, which begin on Sunday? Goran Ivanisevic, Novak Djokovic’s longtime coach, has thought so.“Jannik Sinner, that’s the future,” Ivanisevic said on the ATP Uncovered show in 2020. “For sure, top-five player, maybe No. 1. I can’t say that far, but the kid is 18, hits the ball amazingly quick. He is the deal.”Cahill, along with Sinner’s head coach, Simone Vagnozzi, whom Sinner has also worked with since last year, has helped Sinner grasp the concept of not just hitting the ball hard, but of also using dips, spins and off-pace shots to open up the court and force his opponents to run until their legs give out.The lessons, via video and on court, have paid off. Sinner, an Italian, is ranked No. 4 in the world, up from No. 15 a year ago. He has won four tournaments this year, including his first Masters 1000 at the Canadian Open in August, as well as two of his past four events, in Beijing and in Vienna.Sinner withdrew from the Paris Masters last week after finishing his second-round match at 2:37 a.m. and then being scheduled to play his next match against de Minaur less than 15 hours later. He complained that tournament organizers were not allowing him enough time to recover, leaving his body vulnerable before the upcoming ATP Finals and Davis Cup Final, where he will compete for Italy.After making his ATP Finals debut in 2021 as an alternate, Sinner has qualified on his own this year. He goes in as the fourth seed behind Djokovic, Carlos Alcaraz and Daniil Medvedev and ahead of Andrey Rublev, Stefanos Tsitsipas, Alexander Zverev and Holger Rune. The tournament is at the Pala Alpitour in Turin, Italy, about 300 miles from Sinner’s Northern Italy hometown.Sinner has a winning record against Alcaraz, including victories at the Miami Open and China Open this year. After losing his first six matches against Medvedev, including in the finals in Rotterdam and Miami this year, Sinner has beaten him twice in the last month. In a three-set Vienna final, Sinner saved two set points in the first-set tiebreaker, one with an ace up the middle and flummoxed Medvedev with frequent forays to the net.The only players in the Finals that Sinner has not beaten are the world No. 1 and six-time ATP Finals champion Djokovic, and Rune. Sinner fell to Djokovic in the Wimbledon semifinals this year and in the quarterfinals last year. In the 2022 match, Sinner led by two sets to love before falling in five sets. Against Rune, Sinner lost in Monte Carlo this year and retired because of injury in a match in Sofia, Bulgaria, in 2022.After suffering through some injuries over the past few years, Sinner has dedicated himself to strengthening his body through off-court work with his fitness coach, Umberto Ferrara, and his physiotherapist, Giacomo Naldi.The only players in the Finals that Sinner has not beaten are the world No. 1 and six-time ATP Finals champion Djokovic and Holger Rune. Wu Hao/EPA, via Shutterstock“This year, we made a lot of tough decisions to not play a couple of tournaments because it is very important for me to get a lot of gym work and strength and mobility to get better,” Sinner said. “I feel it on the court that the more the match goes on the more comfortable I feel.”Cahill also sees the value in putting the training first and the tennis second.“A couple of years ago, in a lot of matches, he was breaking down physically,” said Cahill, who is also an ESPN commentator. “He was a late developer, so he just needed to make sure that his body could deal with the rigors of playing at this level week in and week out.”Sinner has, admittedly, struggled mentally with closing out matches, his nerves often getting in the way. At last year’s United States Open, he held a match point while serving at 5-4 to the eventual champion, Alcaraz, in the quarterfinals, but lost the five-hour, 15-minute match 6-3 in the fifth set. The match ended at 2:50 a.m., the latest finish in U.S. Open history. Then, at this year’s French Open, Sinner held two match points in the fourth set against Daniel Altmaier, who saved one of them by hitting a net-cord winner. Sinner lost the second-round match in five sets.Sinner does not travel with a full-time psychologist like many players. Instead, he works with Formula Medicine, an Italian mental-training program sometimes used by Formula 1 drivers.“It’s not like I call them and we talk,” said Sinner, who admitted to being overly competitive in everything from tennis drills to playing cards to go-kart racing. “They give me some exercises to do on the computer. It’s fun to work with them, but you also have to show it on the court. It’s all part of the process.”Cahill sees his role as part technician, tactician and mental guru, often overseeing the work of Vagnozzi, Ferrara and Naldi and helping the team see when Sinner needs to work harder and when he needs time off. Cahill also recognizes the challenge for Sinner at the ATP Finals, especially given that he is the only singles player competing in his home country.“I always encourage my players to have a good look around, to take in the atmosphere, to enjoy it, put a smile on your face and to take the fans for a ride,” Cahill said. “Because, ultimately, that’s all we’re there for. If you think about winning and losing too much, it can be like an anchor around your ankle.”As a child, Sinner played soccer and was a top-level junior skier in Italy. He won a national championship in giant slalom when he was 8 years old. But by 13, he had quit skiing to devote himself exclusively to tennis.“In skiing, it was more that if you make one mistake you cannot win the race, while in tennis you can make some mistakes and still win the match,” he said. “I think that’s the biggest lesson that I have learned from skiing. Obviously, they are two different sports, but maybe the coordination, the balance and the sliding helped me a little bit to play tennis.”Cahill is keenly aware of the pressure that Sinner is facing as he enters the ATP Finals. They have been working on simulating stressful situations and critical points, including using deep-breathing exercises and encouraging Sinner to look across the net and take note of the stress level of his opponent.Two things that Cahill would like to give Sinner, but knows he can’t, are John Isner’s powerful serve and John McEnroe’s meticulous volley. He can, however, give him advice.“Jannik has earned his place in the ATP Finals, and everybody’s there to see him,” Cahill said. “Every single player is an incredible tennis player. So go out and put on a great show and don’t think about the end result. Just be brave and play your type of tennis.” More