Meet Caty McNally, Coco Gauff's doubles partner who took a US Open set off Serena Williams

Serena comes back to defeat 17-year-old McNally (2:09)

Serena Williams drops the opening set to Caty McNally but comes back strong to edge the young American challenger and move on to the third round. (2:09)

It took 46 minutes (and six service games, four aces and a 110 mph serve) for Catherine "Caty" McNally to take the first set 7-5 over Serena Williams on Wednesday in their second-round clash. In front of a packed crowd at Arthur Ashe Stadium, she watched as Williams helplessly hit the ball high and out of bounds. She turned to the sideline, raised her arms up and down as if trying to pump up the crowd, and walked -- bounced, really -- to her chair.

She never smiled.

The 17-year-old did her best to stay composed and focused and act like this wasn't the biggest moment of her life.

"I was just really excited, honestly," she said after the match. "Could you tell from my reaction? I was really pumped up. Super happy just to get a set from her. That's something that not very many people do. But I knew I needed to stay focused because I knew she was going to pick up her level."

Williams, meanwhile, looked stunned as she took her seat, and the crowd was in a frenzy. Who the heck is this girl?

For those who follow tennis closely, McNally has been one to watch for some time. She won the junior title at the 2018 French Open and is the reigning junior doubles title winner at the US Open with partner Cori "Coco" Gauff. The two young stars teamed up again earlier this summer to win their first WTA trophy at the Citi Open in Washington D.C.

Nicknamed "McCoco," the duo will make their Grand Slam debut as a pair this week as well. Insiders have high expectations for both.

Currently ranked No. 111, McNally has been slowly rising in the professional ranks in her first year on tour. Like Gauff, she made it through Wimbledon qualifying and into the main draw, but she lost in the first round. Gauff, for her part, captivated the world with her win over Venus Williams and run to the fourth round. McNally needed until Monday to win her first Grand Slam match, which she took in straight sets over veteran Timea Bacsinszky.

Coached by her mom, Lynn Nabors-McNally, and Kevin O'Neill, whom she has known since she was 4 years old, McNally embraces a looser attitude than perhaps many of her peers. In an interview with the Women's Tennis Coaching Association earlier this year, O'Neill talked about his philosophy and approach to the game. "I mention to Caty all the time that tennis is just a game," he said. "Even though it's professional tennis, it's just a game. If you keep it a game, you can look at things a bit easier and not make it quite as stressful."

When she walked on the court -- waving and smiling as her name was announced like she had done it before -- for the second match of the prime-time slate on Wednesday, she looked almost relaxed. She didn't look like someone playing in her second major match against the greatest player of all time or, for that matter, like someone who hadn't been born when Williams won her first Grand Slam title.

"I just try to take it as another match and not really worry about who's across the net," she said later. "I know if I did that, it might affect the way I play. I might become more emotionally attached to the match. That's not good for me."

Her first set felt almost legendary. Williams had never dropped a set in any of her 18 second-round matches at the US Open. McNally made her do it in her first second-round match at a major.

"It was definitely something to get used to," Williams said after the match of her young opponent's ability. "You don't play players like her that have such full games."

Unfortunately for McNally, Williams did adjust, and she took the next two sets handily 6-3, 6-1. In the third set, McNally earned just five points. However, she fought until the end and never seemed intimidated by the moment. When her once-magical night was over, McNally again showed no emotion and gave Williams a firm handshake at the net.

The outcome wasn't what she wanted, but a smiling McNally was quick to put her night into perspective as she walked into a room full of eager reporters shortly after.

"I'm really just happy with the way I overall played, the way I carried myself out on that stage," she said. "I walked out there, and I had the chills. That was the most insane atmosphere. I've never played on a court nowhere near that big, especially a night match. I couldn't have asked for anything better. It was just an unbelievable experience, something that I'll never forget for the rest of my life."

She'll bring those memories with her when she and Gauff start their doubles campaign later this week.