Cori Gauff and Tseng Chun Hsin were crowned 2018 junior Roland Garros singles champions in Paris. 

Gauff, at 14 the youngest entrant in the singles draw, overcame a nervous start against 16-year-old Caty McNally to win a see-saw all-American girls' final that included fifteen breaks of serve, 1-6 6-3 7-6(1).

"I'm very excited and happy, because this is my first time and this is my first main draw Roland Garros," said Gauff, who had thrown her racket in the air before falling on the clay after securing her first Grand Slam title.

"So it's really exciting to be playing here," she said. "It was a tough fight, but at the end it was worth it."

Gauff becomes the fifth American girls' singles champion in the last seven majors, a run of success that has not been seen since 1980-81. She is the ninth American junior singles champion 'boy or girl' since 2015, according to the US Tennis Association.

Earlier in the day, Tseng, of Chinese Taipei, defeated the top-seeded Sebastian Baez of Argentina, 7-6(7) 6-2 to clinch the Roland Garros boys' title.

In the girls' final, it had initally looked like McNally was on the way to a swift victory after she won the first set in 25 minutes, and began the second with a service break as a dejected Gauff dropped her racket on the clay.

But Gauff, who just like Tseng trains at the academy of Patrick Mouratoglou, the long-time coach of Serena Williams, staged an impressive fightback.

Gauff, who had been playing in her second junior Grand Slam final after she lost to Amanda Anisimova in the US Open final, took the second set in 42 minutes as she finally found her range.

McNally, who had led 3-0 in the decider and had served for the match at 5-4, was unable to finish the job as Gauff fought back to eventually take the match in the tiebreak on her third match point with a forehand volley.

"I just kept telling myself to stay calm, and I can do this," said Gauff. "The night before my cousin texted me, and she said: 'No matter what happens, just say calm and just remember that you can win'. So I just kept thinking about that."

Her experience in New York had helped her in Paris during her second Grand Slam final.

"I remember being nervous at US Open where I couldn't really play," Gauff said. "So I tried not to let myself get there here, even though I was nervous."

Tseng, who shares a birthday with Roger Federer, now also has another thing in common with the 20-time major singles winner: a junior Grand Slam title.

"I feel very happy and excited," said Tseng, who had lost in the final of the Australian Open in January to Sebastian Korda of the USA.

Just like Gauff, Tseng had a nervous start in his second Grand Slam final this season, going down 3-1 in the first set to Baez, the newly crowned No. 1 junior.

"First set I was a little bit tight in the beginning, and after I just enjoy and getting relaxed," Tseng said. "So after, I come back."

After taking the first set with a backhand winner down the line, Tseng celebrated wildly, pumping his fist and jumping in the air. In the second set, he began to dominate a slightly deflated Baez, who started to make some mistakes.

After three love holds, Tseng got his first match point on an error by his opponent as he served at 5-2. After taking the match on a backhand volley, Tseng celebrated with his team, which included his father and Mouratoglou.

Tseng, who has been practising at the Mouratoglou Tennis Academy, received a long hug from the Frenchman afterwards.

"He has been supporting me for many years," said Tseng about Mouratoglou. "He wants me to play aggressive on the baseline. Today I was playing really well on the baseline and solid."