Francis Tiafoe reacts after giving up a point to Evgeny Donskoy during the first round of the Citi Open, an event the Riverdale Park native says he would attend growing up. (Toni L. Sandys/The Washington Post)

Francis Tiafoe retreated to the depths of Stadium Court at William H.G. FitzGerald Tennis Center on Monday hours before his first-round match at the Citi Open. The crowd at the tournament was already full of people who wanted to wish Tiafoe well before his first ATP Tour main draw match.

Some had played with the 16-year-old Riverdale Park native in various junior tournaments around the District. Some had seen him play when he was younger. Some had only heard of him and were already fans.

Tiafoe just wanted to be alone on the treadmill to stay focused. But when he was announced on Stadium Court for his match against Evgeny Donskoy of Russia under the lights, the crowd was with him, raucously applauding. Despite losing his match in straight sets, 6-4, 6-4, Tiafoe said the match meant more to him than anything he’s done in his tennis career.

“Walking on the court, the crowd started going crazy,” Tiafoe said. “I almost cried.”

With each point, the crowd cheered the world’s sixth-ranked junior player. Chants of “Francis” and slow claps erupted throughout his first set. He got broken early, falling behind 3-1 despite flashing a serve that reached upward of 120 mph. His twin brother, Franklin, nervously moved around from one section of the stadium to another.

Tiafoe slides across the baseline after going for a ball hit by the Russian Donskoy, who prevailed in straight sets. (Toni L. Sandys/The Washington Post)

The second set was more contentious with the players trading breaks. A long rally saved break point in the first game, getting Tiafoe’s coach, Misha Kouznetsov, out of his seat in applause. Tiafoe broke Donskoy in the fourth game of the second set to even it at two games apiece.

But then Tiafoe was broken in the seventh game, giving Donskoy a 4-3 edge that the Russian didn’t lose as he held serve for the rest of the set. Donskoy, ranked No. 111 on the ATP Tour, said he was impressed with Tiafoe’s game and could see him being a talented player in the future.

In the present, though, Kouznetsov remained pragmatic.

“He made a couple of poor choices on a couple of shots, and he wasn’t able to hold serve enough,” Kouznetsov said. “You’re supposed to hold serve at this level. If he were to hold serve more and maybe not double fault here and there, then he would have been able to at least go three sets.”

Tiafoe said he was expecting the crowd support, and he had a feeling his match would be on Citi Open’s Stadium Court. He’d grown up going to the event every summer, and he said he would dream of playing in the tournament.

Tiafoe wasn’t the only junior making his ATP main draw debut. Seventeen-year-old Jared Donaldson played Rajeev Ram, both Americans who qualified for the tournament over the weekend. Donaldson won his first set, but dropped the next two, falling, 6-7 (7-1), 6-4, 7-5. Donaldson will also play doubles this week with Stefan Kozlov, their first-round match scheduled to be against the accomplished Bob and Mike Bryan.

Donaldson’s youthful exuberance showed throughout the match, as he repeatedly argued with the chair umpire and muttered expletives under his breath in frustration when a point didn’t go his way.

“It’s a learning experience, and hopefully I’ll get more experience and more used to the feeling of playing in an ATP event,” Donaldson said. “It was my first round, so hopefully that will come with time.”

Both Donaldson and Tiafoe entered the tournament as feel-good stories, both with nothing to lose because expectations were low. Tiafoe said seeing other young Americans perform well motivates him because he feels they’re always trying to one-up each other, pushing each other forward in the process.

“I think the game is going to start changing in the next couple of years,” Tiafoe said. “Younger guys are going to start taking over again.”

For Tiafoe, part of the learning experience was getting to be around pros and acting like one himself, something he hopes to continue going into the 18-year-old national championships in Kalamazoo, Mich., next week and then U.S. Open juniors. For Donaldson, getting a taste of ATP Tour tennis will play into his decision on whether to turn pro over the next 18 months.

“American tennis needs more of this,” Kouznetsov said of Tiafoe’s match. “A little more of this with a more complete game, and he’ll be older and stronger. Then boom, hopefully we’re there.”