After all these years, Serena Williams -- defying the laws of physics that keep the rest of us tethered to this Earth -- is still The One.
More than three centuries ago, Sir Isaac Newton identified the concept of gravity: What goes up must come down. Not Serena -- not quite yet.
She turns 35 in about a month but still finds herself the WTA's No. 1-ranked player, the oldest ever to occupy the top spot. This, more than 14 years after first ascending to the throne, displacing older sister Venus in 2002.
Despite her relatively advanced age, Williams can make some significant history at the incoming, upcoming US Open.
Last month, Serena collected her 22nd Grand Slam singles crown at Wimbledon. A title in New York would be No. 23, breaking a tie with the great Steffi Graf, creating a new Open era standard. That would also extend her streak of consecutive weeks at No. 1 to 187 -- breaking Graf's long-standing record by one.
Tennis Channel analyst Mary Carillo, just back from a stint in Rio for NBC, sees similarities between Serena and a certain heavily decorated swimmer.
"I point you to Michael Phelps," Carillo wrote in an email, "who like Serena accomplished everything an athlete dreams of leaving behind -- records, gold, best-ever acclaim -- and still was driven to do more. My guess is that Serena never imagined she would still burn to be great at nearly 35 years old, just as Michael never dreamed he'd still be wet and wondrous at 31.
"Both of them, still willing to do the work it takes to be who they are."
How has the ageless Serena managed to do this?
Eighteen-time Grand Slam champion Chris Evert, who spent 113 weeks at No. 1, answered the eternal riddle with this succinct email: "Exceptional power, exceptional athlete, still motivates herself chasing history."
Indeed, at an age when most players begin to lose their competitive edge, Serena accelerated through her early 30s.
Mary Joe Fernandez, who coached the U.S. Olympic tennis team four years ago in London and again in Rio de Janeiro, traces this unlikely renaissance to a brutal stretch in 2010-11 that forced Williams to miss three consecutive majors. After winning Wimbledon in 2010, Serena suffered a serious cut when she stepped on broken glass in a restaurant. In March 2011, a blood clot in her lungs morphed into a condition that was termed life-threatening.
"Her health scare gave her an appreciation for what she does and recommitted her to being the very best," Fernandez said earlier this week. "The last three, four years she's been playing more, being as fit as possible.
"She's been great from the start, and now we're seeing her great on a consistent basis."
After those three Slams absences, Serena failed to win a title in her next four tries. And then, she won the last two majors of 2012 -- and a total of nine of 17. All after her 30th birthday.
For context, consider the next women in line in that Open era category: Martina Navratilova and Margaret Smith Court won three each past 30, while Evert and Billie Jean King scored two. Only four men have won more than one -- Australians Rod Laver and Ken Rosewall, with four each, and Andre Agassi and Jimmy Connors with two.
In 2005-06, ankle and knee injuries forced her to miss three of six majors and ultimately knocked her out of the top 100, adding another subtle layer to her powers of perseverance.
Pam Shriver, a 21-time Grand Slam doubles champion, believes Serena's time away from the game and the addition of coach Patrick Mouratoglou helped extend her career.
"For the entire body of work, from the time she picked up her first tennis ball to now, she has never over-competed," Shriver said. "So she's still eager to play late in her career. And then, after only having parents as coaches, Patrick comes in and not only brings technical and tactical expertise, but was an enormous boost to her psyche, which created even more motivation.
"That was perfect timing for both."
Considering her historically high standards, it's been a mixed bag for Williams this year. She made the finals of the season's first two Slams but lost to Angelique Kerber in Melbourne and Garbine Muguruza in Paris.
The win at Wimbledon was the high point. In Rio, she lost her third singles match to Elina Svitolina and crashed out in the first with Venus in doubles.
An injury to her right (serving) shoulder, according to Fernandez, was the culprit.
"The first day of practice in Rio, she was hitting easy serves, then tried one a little faster," Fernandez said. "She stopped and said, 'It still hurts.' I told her to stop serving, and she didn't hit another one until her first match."
Serena accepted a wild card into last week's Cincinnati tournament, but eventually withdrew. That gives her an extra week to rest the shoulder, but no one -- perhaps even Serena -- knows how ready it will be for seven potential matches in New York.
Shriver, who will also be part of ESPN's first-to-last-ball US Open coverage, starting Monday at 11 a.m. ET on ESPN3 (and 1 p.m. on ESPN2) has some insight into sore shoulders. During 19 years, she had two shoulder surgeries -- and nearly a third after a recent mother-son tournament. Shriver attributes Serena's soreness to inconsistent tosses that put more stress on the shoulder. And that leads to more practice, which considering how hard she hits the ball, causes even more wear and tear.
"I don't pretend to know what the injury is, exactly," Shriver said. "But from a distance, I would seem like if it wasn't major an athlete two weeks before a major got a cortisone shots and rested properly, she could be ready to go. I had three, and the results were amazing.
"The shoulder is a big question mark. If she doesn't have her best serve, she becomes an average player among top-10 players. All the confidence and intimidation that serve -- the best in the history of women's tennis -- brings is in jeopardy. If she doesn't have it, she's not my favorite to win."
Serena might need to win the US Open to retain her No. 1 ranking. Kerber could have taken it with a victory in the Cincinnati final but fell to Karolina Pliskova. Heading into New York, Serena leads Kerber by 190 points, 7,050 to 6,860. The winner gets 2,000 points.
Serena, who is defending a semifinals appearance (780 points), will have to advance further than Kerber, who is only defending a third-round effort worth 130 points. Williams will have to reach the semifinals and possibly further to keep her No. 1 ranking. If Kerber advances to the quarterfinals, Serena would need to make the finals. If Williams wins the US Open, she will stay on top. If the two meet in the final, the winner emerges No. 1.
Technically, two other women, Muguruza and Agnieszka Radwanska, could also move into the No. 1 spot.
For Fernandez, it's not Serena's long-term presence at the top, but her utter domination of the sport across a dozen years.
"It's one thing to have longevity in an athletic career," Fernandez said. "But longevity at the top, that's unheard of.
"The older you get, the more it means because you know the window is closing."