NEW YORK - 2017 champion Sloane Stephens advanced to the third round of the US Open with a dominant 6-4, 6-2 win over No.21 seed Coco Gauff in 66 minutes. With the roof closed on Arthur Ashe Stadium, Stephens saved the sole break point she faced to go unbroken against the 17-year-old American, moving her record in the second round of Slams to an impressive 24-3.

This was the first career meeting between Stephens and Gauff. Now ranked No.66, Stephens' form had been trending up since the start of the clay season this spring. On clay, the 2018 French Open finalist made the Charleston quarterfinals, Parma semifinals and Round of 16 at Roland Garros. Since the clay season, small margins have stalled her results but not her form. Her last four losses have been hotly contested three-setters that came down to the wire. 

Stephens' fortunes changed right away in New York. Drawn against her best friend Madison Keys in the first round, a rematch of the 2017 US Open final, Stephens edged Keys 6-3, 1-6, 7-6(7) in a high-level contest. 

"I've had to battle two good friends," Stephens said. "I think the pressure is a little bit different when you play two people that you know well. It's a different type of pressure. Obviously playing here at the US Open and playing Americans, it's very different.

"But I'm really happy with the two wins. I played good tennis to get them. I mean, it's still only the third round of a Slam so I have to keep going. But it's nice to know that I was able to get those two wins with all the pressure and outer things happening."

How the match was won: Little separated the two through the first set, as Stephens and Gauff rolled through their early service games, combining for four love holds through the first eight games. But serving at 4-4, Gauff fired three unforced errors, including a double-fault at 15-40 to hand over the first break of the match. Serving at 5-4, Stephens closed out the set by out-rallying Gauff in a 13-shot rally that ended when the young American misfired on a backhand.

Gauff earned her only chance to break the Stephens serve early in the second set, but the 2017 champion's serve proved impervious on the night. Serving at 2-2, 30-40, Stephens placed a 108 mph unreturnable first serve and followed it with another wide serve to earn game point, which she converted. Serving well over 80% for most of the match, Stephens would lose just 10 points on her serve all night. In contrast, while Gauff possessed the bigger serve, the younger American struggled to protect her second serve, winning just 38% of second serve points. 

Having saved break point, Stephens ratcheted up the return pressure. Gauff misfired on her third double fault of the match to open the 2-3 game and Stephens continued her heavy, deep hitting to push Gauff well behind the baseline and earn a break at love. The former World No.3 would run off the final four games to book her spot in the third round.

Stat of the Match: Unbroken on the night, Stephens served at 84% for the match and held at love in five of her nine service games. "

"I knew I wanted to place a lot of first serves and get myself started early in the points," Stephens said. "Serving that high percentage for me is always really key just because I can get into the points and I can start off aggressive with me dictating play, which is what I want to do. That was just part of it. But happy and very pleased with that stat."

Stephens on Gauff: "I think the last time we hit, she was probably 12. It was a little bit different. I don't know why, we just never really have practiced on tour. I wasn't too familiar. Obviously I've seen her play. I know her game well. We trained with the same coach for a long time. We kind of have similar things that we do, which is interesting.

"But as her game has evolved ... Obviously she's only 17, so she has a long ways to go. I think just being able to see it, I feel old. She was at my 21st birthday. I'm now 28. 

"It's just been really nice to see her game kind of evolve and the things that she's doing, like how she's able to turn so much defense into offense and kind of do those movements. She is great at the net. She has a really great all-around game. It's been really nice to see. She's different from a lot of the up-and-coming players we're seeing now that are just super hard-hitting, not much variety.

"She has a lot of variety. I think a lot of the younger girls, there's half that are very hard-hitting and half that have a lot of variety. I think she's in the bucket with a lot of variety."

Next up for Stephens: Stephens joins Danielle Collins as the two Americans in the third round of the bottom half of the draw and will face either 2016 champion Angelique Kerber or Anhelina Kalinina. 

The second-round match between Kerber and Kalinina was postponed due to rain. Weather permitting, the match will be played on Thursday.