Naturally, for someone who has won 17 grand slam titles, it's an obsession with her sport that continues to stoke the fires.
Williams's crazed jumping up and down celebration - all the poise of your uncle at a wedding - after beating Victoria Azarenka in the final for the second successive year here proved that the thirst for battle and the roar of an appreciative crowd continue to galvanise. It may be 14 years on from her first major title in the very same arena, yet this felt every bit as special.
It was close, much closer than before, the Belarusian having recovered superbly from 4-1 down in the second set to prise the first set Williams has dropped in the tournament but she was unable to stop the home favourite from running out a 7-5, 6-7, 6-1 victor in the best women's match by far here over the past fortnight.
After pocketing $3.7m - it included a $1m bonus as reward for her supremacy on the North American hard court swing - the 31-year-old joined an elite band in the sport to have broken the $50m mark in prize money. Only Roger Federer, Rafa Nadal and Novak Djokovic had beaten her to it.
Williams is fourth on the all-time list of women major winners in the Open era, one behind Martin Navratilova and Chris Evert and five adrift of Steffi Graf, the most successful woman of all time with 22 grand slam titles. Her 17th also brought her level with Federer.
Yet, you would find plenty of takers for the notion that the American is greatest of all. In these modern times, players are fitter than ever, the demands are greater and the schedules packed like never before. Her consistency is breathtaking. She is only the fourth female in the open era to have contested at least 20 major finals and has won four of the past six slams. Only Martina Navratilova (306) , Chris Evert (299) and Steffi Graf (278) have won more matches in major tournaments than the 31 year-old (246).
With the numbers come the money, although there is only one thing which Williams really cares about. "I never, never, in my life have picked up a cheque. I don't play tennis for the money. I honestly love to play. I love grand slams," admitted the world No.1.
"When I grew up playing tennis in Compton, I just never thought about any of this. I didn't think about the press. I didn't think about I didn't even know all this came with everything. I think my dad got me into tennis because of the money but, me being naive and silly, I never thought about it."
Of her 17th grand slam title, she commented: "It's an honour to be even with Roger. He's been such a great champion throughout the years, and he's just an unbelievable competitor; he's still playing and he can probably still win more.
"It feels really good to be, you know, in that same league as him. He's just been so incredibly consistent, so we have had really different careers. Then to be compared with Chrissie [Evert] and Martina [Navratilova] . . . not yet, because I'm still not quite there yet. I can't necessarily compare myself to them, because, you know, numbers wise they're still greater."
Looking at the rest of the field, it seems natural to assume Azarenka will contest with Williams again at this stage the next time a major comes around.
There is a steel in her soul, never more evident than when the 24-year-old mounted that comeback in the second set as conditions, and her opponent, were threatening to blow her away.
With age on her side and with experience already in the bag, the world No.2 will surely get better. She showed that, while she has the power game to cope with the queen of Flushing Meadows - unfortunately for the Women's Tennis Association, there are very few who can - the need to stay strong for longer needs to be improved.
"She is a champion and she knows what it takes to get there," said Azarenka, the reigning Australian Open champion. "I know that feeling, too and, when two people who want that feeling so bad meet, it's like a clash. That's what happened out there. There wasn't much between us so I am going to work my ass off and come back stronger.
"I think when you have a bigger challenge in front of you in anything in life or, you know, in any practice, you try to be better. She's my biggest challenge. Every time I play I need to raise that level because, in some matches, even though you're not playing your best, you find a way to work through it and win ugly sometimes. With her, you have to rise to the occasion.
"I always will look for the opportunity to play against the best player and test myself. After that, as I'm going to do today or tonight or in two days or whatever, I'm going to reassess on what other things I want to improve. I already have a pretty clear image."
Right now that picture is of Serena Williams holding aloft the US Open trophy for a fifth time. There cannot be any greater motivation than that.