She looked very different from the player who took the court at Flushing Meadows in past years, yet exactly the same. And that is how Williams is dominating tennis as she nears her 32nd birthday.
She has figured out how to play passionately and placidly all at the same time.
"Even yesterday, I was still complaining. You could see that I'm throwing my hands everywhere," Williams said Monday. "That's just me. I'm never going to be able to change it. I just have to learn how to hold that in a little bit — but still be myself."
She unraveled in the second set, lost the first two points of the third, then mastered that tricky balancing act the rest of the way. The top-ranked American beat No. 2 Victoria Azarenka 7-5, 6-7 (6), 6-1 for her fifth U.S. Open title and 17th Grand Slam championship.
Williams assumes that wobbly second set — when she twice failed to serve out the match — came from the nerves of knowing she was on the verge of history.
"In the third, I didn't care," she said. "I was just like, 'This is what's going to happen; this is what I'm going to do, and this is going to be the result.'"
Fourteen years after her first U.S. Open title, Williams' experience had one thing in common with her victory at age 17: She didn't do much celebrating that night either time.
In 1999, it was because she was too young. In 2013, she was too tired after two weeks of playing singles and doubles.
Williams said she ordered room service, then tried to fall asleep, but wasn't very successful at that.
She feels fresh mentally and physically and is surprised on both fronts. There are a few aches and pains, but nothing that a few days of rest won't fix.
And after playing an unusually busy schedule by her standards, Williams doesn't yet sense the need to take some time off. That's a change from earlier in her career.
She won her 500th career match at the 2012 Australian Open and insists it felt as though she notched No. 600 two weeks later. In fact, it was at Wimbledon this year — a quick accumulation nonetheless.
She might not enter as many tournaments next season. Williams had been chasing the No. 1 ranking; now she wants to focus on the four Grand Slams, though she realizes that sometimes winning the smaller events can lead to titles in the bigger ones.
Her priorities were obvious when she was asked to evaluate her 2013, with a career-high nine titles overall. Last year was better, Williams explained, even if she won fewer tournaments. The difference? In 2012, she captured two Grand Slam championships and an Olympic gold medal. That outweighs her two major titles of this year.
Williams is particularly proud, however, of her 2013 French Open victory, her first since 2002.
She likes how doubles helped her stay calm and focused the last two weeks and hopes to play in more events with sister Venus during the tour's Asia swing in the fall.
For all of Williams' success under current coach Patrick Mouratoglou, she believes her improvement since they began working together 15 months ago can be partly traced back to her first coach, her father.
"My dad gave myself and my sister a game that you can always grow, you can always build on, you can always improve," she said.
In winning four of the last six Grand Slam titles, Williams has taken the best of the player who pumps her fist and shouts "Come on!" after a big winner and added the poise of a veteran who doesn't crack when a call goes against her. As the ebb and flow of Sunday's final reminded, with the swirling wind and Azarenka's counterpunches rattling Williams at times, that fusion is difficult to achieve. But when it is, the result is impeccable.
"If I'm too competitive and I'm too excited, then it doesn't go well for me. I get too tight," Williams said. "Or if I'm too relaxed, then I don't have enough energy, and that doesn't work out, either. So it has to be the perfect blend."
Williams' tirades at the 2009 and 2011 U.S. Opens seem like fuzzy memories after consecutive three-set victories over Azarenka in the final. The Arthur Ashe Stadium crowd was fully behind her Sunday.
Williams is one major title behind Martina Navratilova and Chris Evert. Catching them might appear inevitable with her current play — not just because she's serving and moving so well, but because she still finds ways to win when her game deserts her.
"I always say it's really about how you can come back from the downs that really can describe you as an individual, as a champion, as a person," Williams said. "It's not how well you do when you're high, and everyone's awesome, and everyone's happy for you and everyone's writing about you, and it's only positive things. That down definitely comes."