NEW YORK -- Coco Gauff’s first major appearance at this US Open came late last week at Media Day.

“How is your August going?” the interview moderator asked glibly.

“Oh, semi,” Gauff said, smiling. “Not too bad.”

Like so many teenagers, Gauff has a great facility for understatement.

On Monday night, with Michelle and Barack Obama in the house, Gauff at times looked, well, presidential, treating the Arthur Ashe Stadium crowd to a contentious, rollicking 3-6, 6-2, 6-4 victory over German qualifier Laura Siegemund. The 2-hour and 51-minute tussle came down to the wire.

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And so, the month that began with a routine victory over Hailey Baptiste in Washington D.C. will end with Wednesday’s second-round match against Mirra Andreeva, a 1-6, 6-3, 6-4 winner over Australian qualifier Olivia Gadecki.

Gauff has played 13 matches in the North American heat, won 12 of them (dropping only four sets) and collected the two biggest titles of her career. In Cincinnati, Gauff ended a 0-7 mark against World No.1 Iga Swiatek on the way to her first WTA 1000 win -- and emerged as a serious threat for her first Grand Slam victory.

“August has been a great month for me,” Gauff said. “I’m really excited to go into the rest of this month -- hopefully a little bit into September, as well.”

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There are five teenagers among the Hologic WTA Tour’s Top 100, with Gauff, 19, the highest-ranked at No.6 and Andreeva, 16, the youngest. Not only will the future of professional tennis be on display but, one could argue, also a healthy blast of the present. The two faced off at the French Open this spring. Gauff engineered another three-set comeback to win 6-7(5), 6-1, 6-1.

Gauff, in what feels like one of those time-lapse videos of a plant flowering, has suddenly blossomed into everything that has been imagined since she bolted into the fourth round four years ago at Wimbledon at the age of 15.

In essence, Gauff is starting to trust her phenomenal instincts. At the age of a typical college sophomore, she’s learning to win while not playing her best. Maybe it’s a coincidence, but the newest coaching addition to her team, Brad Gilbert, once wrote a book called “Winning Ugly: Mental Warfare in Tennis -- Lessons from a Master.”

“I think for me with BG, I think I have a lot more confidence in my game,” Gauff explained. “I think hearing it from someone who probably has seen countless of my matches, I think you just really believe it. Sometimes I’ll be practicing, maybe practice points with another player, it’s 30-All or deuce, he’ll say something completely random like a joke or something.

“It’s just little things like that that made me realize that tennis is serious but it’s not as serious as sometimes my head makes it out to be. I feel like no matter the score line in the match, I [am] able to problem solve and troubleshoot my way out.”

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The most recent example: the first game of the second set. Siegemund had put down a terrific first frame, beating Gauff to virtually every punch, and suddenly the transcendent teenager was looking a tad tentative. That was when Gauff launched into hyper mode.

In a game that required 12 deuces and ran 26 minutes long, Gauff converted her eighth break point when Siegemund put a forehand into the net. It was an extraordinary game, and gave Gauff some badly needed momentum. Converting her third set point, she raced into the decider that, seemingly, had already been decided. Gauff led 5-1 before Siegemund came storming back to to 5-4, but the teenager finally closed things out with a clutch first serve and a missed backhand from the German.

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"I definitely won ugly tonight," Gauff said. "It was a lot of weird points, with the slicing. Usually something that I usually do well against, opponents who slice. We were prepared for it. I think today was just execution."

Gauff reached the fourth round at the Australian Open and the quarterfinals at Roland Garros, where she was a finalist the year before. But her real takeoff came directly after a devastating first-round loss at Wimbledon; qualifier Sofia Kenin sent her awkwardly out of the draw with a three-set victory.

“I think the mindset is different,” she said. “Having that first-round loss at Wimbledon shows that it wasn’t really as bad as it could [be], so I’m not going into this tournament worried if I lose early or not. I think now I’m going in with a lot more confidence.

“I feel like no matter the score line in the match, I can problem solve and troubleshoot my way out. I know I can win matches not playing my best game now. I think I wasn’t playing my best in every single match in D.C. and Cincinnati, it's impossible. I do feel I’m much more confident in my B or C game. I think the most I’ve learned over the course of this summer is that I don’t have to play A-plus tennis to win.”