She exited the match brimming with confidence after threatening an upset of the 37-year-old American superstar before Williams rallied for a 5-7, 6-3, 6-1 second-round triumph.
“That was unbelievable,” McNally said. “I came out really strong. I felt really good out there actually on the big stage. I wasn’t too nervous.
“The first set was unbelievable tennis. I played really well, served really solid. The second and third set, she obviously picked up her level. That was pretty tough for me.”
Williams won her first Grand Slam title at the 1999 US Open and even reached her second Slam final in 2001 before 17-year-old McNally had been born.
“When I went out there, I just worried about myself, but obviously I knew I was playing against the greatest of all time,” McNally said.
“I knew that I had to bring a certain level. I’m really just happy with the way I overall played, the way I carried myself out on that stage.
“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.”
It taught McNally she is already playing at a level where she can compete with the best in the sport, and she isn’t even out of high school yet.
“It just shows I’m capable of playing with the best — I got a set off Serena Williams,” McNally said. “Had her close in the second set, too. Had some chances.
“It just gives me a lot of confidence, shows me that I can compete out on the biggest stages. Just keep my head down, I’m ready to go back to work.”
And McNally is already thinking about how to match Williams when she lifts her level to dominate, as she did in taking nine of the final 11 games.
“Next time,” she said. “I just have to raise my level with hers.”