Francis Tiafoe won his second-round match against Yunseong Chung of Korea, but lost in the the third round Thursday. (Matthew Stockman/Getty Images)

After an error brought him within two points of conceding the opening set of his third-round match at Wimbledon’s Junior Championships, Francis Tiafoe bashed his racket on the grass court and drew a warning from the chair umpire.

He lost the set in a tiebreak.

Then, after leveling the match at one set apiece only to fall behind in the third set, Tiafoe blasted a ball out of the court upon committing another gaffe. For that, he was docked a point that handed fellow American Noah Rubin triple match point.

From there, the 18-year-old Rubin rolled to a 7-6 (7-4), 4-6, 6-3 victory that landed him in Friday’s quarterfinals.

Tiafoe, 16, will head back to Riverdale Park without a trophy of any sort, bounced from the junior doubles event later in the day when he and fellow American Michael Mmoh were ousted by an unseeded Brazilian duo, 6-1, 7-6 (16-14).

Francis Tiafoe literally grew up around tennis, often spending nights at a Maryland tennis center where his father worked. At only 16, he is ranked number two in the world. Could a future U.S. champion be in the making? (Lee Powell/The Washington Post)

The 6-foot-1 Tiafoe flashed his considerable upside in the three singles matches he contested in his Wimbledon junior debut this week and in the two he played in last month’s French Open junior event, where he was the No. 1 seed. He boasts a pro-caliber forehand and a potent, if occasionally erratic, first serve.

But he was stopped short in both tournaments by bouts of inconsistency and immaturity, which took the form of negative body language on which opponents feast and emotional outbursts at critical junctures.

Frank Salazar, coach of the top juniors at College Park’s Junior Tennis Champions Center, where Tiafoe has trained since childhood, said he planned to discuss both with the junior, who has slipped from No. 2 in the world among boys 18-and-under to No. 8 in the past five weeks.

“Part of maturity and part of being a champions and honoring the game and respecting the game is being able to control your emotions,” Salazar said. “You’re not going to see Federer or Nadal or any of those guys knock a ball out of Center Court.”

Salazar added that he had no doubt Tiafoe has the tools to contend for Wimbledon’s junior title next year. But between now and then, he added, the youngster needs to focus on fundamentals. Chief among them: concentrating, making shots he ought to make, moving his feet, landing first serve and keeping his body language positive.

Patrick McEnroe, general manager of pro player development for the U.S. Tennis Association, offered a similar analysis after watching the match.

“Certainly he needs the maturity, and it’s going to come,” McEnroe said. “He’s only 16.”

Tiafoe was among seven American 16- and 17-year-olds to reach the final 16 in Wimbledon’s boys’ event. On Thursday, three advanced to the quarterfinals: in addition to Rubin, who is from New York, Stefan Kozlov, 16, of Pembroke Pines, Fla., who recently supplanted Tiafoe as the top-ranked American boy; and Californian Taylor Harry Fritz, 16.

Tiafoe has garnered the lion’s share of publicity, featured in The Washington Post, Sports Illustrated and in segments broadcast by NBC and CBS. McEnroe suggested it may have proved a distraction.

“There is maybe too much hype around him, so I think it’s understandable,” McEnroe said. “The key for Francis is to learn from the French and from Wimbledon and say, ‘Okay, here’s the things I need to do better,’ and work on them.”

In an interview after both defeats, Tiafoe conceded he shouldn’t have lost control of his emotions.

“By that time, I thought that match was pretty much going his way,” Tiafoe said. “I wasn’t returning great. He started serving really well. I could feel like the match was slipping; kind of let that go. I knew the point penalty was coming. At that time, you have to say congrats to your opponent.”