WHAT HAPPENED: Frances Tiafoe has another Grand Slam main-draw match to add to his growing stack of “learning experiences” against some of the world’s top players.

No. 22 seed Viktor Troicki of Serbia provided the lesson Tuesday during their US Open first-round match, topping the up-and-coming young American, 7-5, 6-4, 6-3.

Tiafoe, who was playing in his second Grand Slam main draw, was broken five times against Troicki, who blistered 47 winners and committed only 19 unforced errors.

Troicki was playing in his first US Open since 2012, but he looked comfortable on Court 11, taking care of Tiafoe in exactly two hours. Troicki served well, winning 74 percent of his first-serve points. He also dropped 17 aces, compared to Tiafoe’s five.

Few expected Tiafoe to excel at this year’s US Open, though. At 17, he is the youngest player in the main draw and was making his US Open main-draw debut. Tiafoe played in his first Grand Slam main draw at the French Open earlier this year, where he lost in straight sets to Martin Klizan of Slovakia.

Tiafoe received a wild card into the US Open main draw by winning the USTA Boys' 18s national title in Kalamazoo, Mich. The stacked field featured some of the world’s best juniors who happen to be American, including 17-year-old Stefan Kozlov, who turned pro in 2013; Reilly Opelka, the 2015 Wimbledon boys' champion; Taylor Fritz, the ITF world No. 1 junior; and Tommy Paul, the French Open boys' champion who also qualified for this year’s US Open.

WHAT IT MEANS: Troicki can forget about his six-match losing streak. He reached the fourth round at Wimbledon, matching his career-best showing at a Grand Slam. But he hadn’t won a tour match since beating Dustin Brown in four sets at the All England Club.

If Troicki continues to play well, he has a favorable draw. He will face either No. 88 Rajeev Ram or No. 133 Ryan Harrison next. And in the third round, Troicki could face either Donald Young, who beat the No. 11 seed Gilles Simon, or Aljaz Bedene, the No. 57 player in the world.

THE QUESTION: How soon before Tiafoe wins these matches?