Frances Tiafoe reacted as though he had just won the U.S. Open, covering a grin with his hands in disbelief. He actually had just lost a point when his opponent, Marton Fucsovics of Hungary, threaded a forehand between the umpire’s chair and the net post from off the court for a winner. “He nailed it,” Tiafoe said. “I knew he was going to go for it, and I couldn´t believe he made it.” Tiafoe lost the point but won the match Saturday, dominating Fucsovics 6-2, 6-3, 6-2 to become the only American man to reach the second week of the tournament. Ranked 82nd, Tiafoe advanced to the fourth round, his best showing at the Open. “I knew this was big to get to the second week,” Tiafoe said. “I really wanted to keep this run going.” His opponent Monday will be No. 3-seeded Daniil Medvedev, last year´s runner-up. Medvedev won when they met in the first round of the Australian Open in January. “He’s a tough out, and he’s confident right now,” Tiafoe said. “He’s playing the best tennis of his life. But I feel like when I’m playing like I’m playing right now, I’ve got a chance against anybody in the world. I’ve felt that way for years, and I’m starting to finally put it together again.” The 22-year-old Tiafoe has been ranked as high as 29th, but like many young American players, he has lacked the consistency needed to crack the sport’s top tier. He envisions better days for U.S. men, himself included. “I think American tennis is in a great place right now,” he said. “The young guys are all in a great place. In a few years or even sooner, guys are going to be ready to be in second weeks more readily.” Tiafoe said it was “scary” how well he played against Fucsovics, aside from the rally that immediately became a tournament highlight on social media. “I could have hit down the line for a winner,” Tiafoe said. “But I had to go for the fancy shot.” His angled forehand sent Fucsovics scurrying off the court to whack an improbable winner. Tiafoe was still laughing about it when he sat down during the ensuing changeover. Said Fucsovics: “At least I won the point of the match.”