NEW YORK -- Thirty-three years ago, they were born six weeks apart. And yet they are creatures from starkly contrasting environments.
Roger Federer, a child of modest privilege, left home at the age of 13 to learn the game at one of the best tennis academies in Switzerland. Serena Williams came straight out of the public courts in Compton, California. Stylistically, they could not be more different; Federer wins with finesse, while Serena is pure power. Are they the smoothest and the strongest in the history of their sport?
And yet, remarkably, they have arrived at the same place, at the pinnacle of their sport. Both Federer and Williams have won 17 Grand Slam singles titles. Since 2000, there have been only three years when one of them didn't win a major.
Which begs the tennis question of our generation: Who has had the better career?
Construct a graph that charts the veering vectors of their respective careers. Make the vertical line major titles, and the horizontal the 15 years they have been winning majors.
Serena starts fast as a 17-year-old, breaking through right here at the 1999 US Open, beating top-seeded Martina Hingis in straight sets. She actually wins five Slams (including four in a row over two years) before Federer -- who didn't even qualify for Serena's debut Slam -- wins his first, at Wimbledon in 2003.
And then Federer goes off on the sport's most sustained run of excellence. Beginning with that first crown at the All England Club, Federer wins 16 of the next 27 Grand Slams, concluding with the 2010 Australian Open. Put another way, for a period of nearly seven years, Federer wins five more majors than the rest of the field combined.
Serena, who also won at Wimbledon in 2003 (one of five times they've won the same title), then proceeds to cool off. She wins only one major of the next 13 contested, missing five with injuries. And then, after Federer begins to fade after his brilliant run, Serena picks it up again. She wins 10 Slams between 2007 and 2013 -- winning two in a season four times.
Now, perhaps appropriately, they find themselves in a dead heat. With Federer's loss to Marin Cilic, Serena alone has a chance here at the US Open to win No. 18.
While, the major title total is equal for now, all other things are not.
Let's compare some career numbers:
• Federer, because of his consistency and ability to stay healthy, has won about 300 more matches than Serena.
• Federer has spent 302 weeks as the No. 1-ranked ATP World Tour player -- including 237 in a row -- nearly 100 more than Serena.
• Federer has won 18 more titles, 80 to 62, and won nearly $30 million more in prize money.
While Federer has amassed some serious gross numbers, Serena holds an edge in quality; her winning percentage is 85 percent, 4 percent better than Federer's. And though Federer has an Olympic gold medal in doubles (2008, Beijing, with Stan Wawrinka) and a singles silver from London, Serena has four gold medals.
In some minds, the X factor of doubles swings the vote to Serena. She and sister Venus have won 13 Grand Slam doubles titles.
Then again, there's Federer's consistency. He's playing in his 60th consecutive Slam, a record for the Open era. He hasn't failed to show up for work at a major for 15 straights years and counting. Serena has missed 11 Grand Slams going back to 1999. And then there are Federer's mind-bending numbers for consecutive major semifinals (23) and quarterfinals (36).
Federer has reached all four Grand Slam finals in the same year -- and he did it three times, 2006, 2007 and 2009. Serena, not once. Federer has also never retired from a match, a number in excess of 1,200.
Serena supporters will point to her dominance over her peers. Her 17 Grand Slam singles titles, if you remove Venus' seven majors from the equation, are one more than all other active players combined. Federer? He's got 17, but Rafael Nadal has 14 and Novak Djokovic has seven.
Speaking of Rafa, there's this conundrum: Although Federer is widely viewed as the greatest player of all time, his head-to-head record against Nadal is 10-23. The mark is 2-9 in Grand Slams. Maria Sharapova, probably Serena's best contemporary rival, has five major titles, but hasn't beaten Serena in nearly 10 years and a string of 15 consecutive defeats.
What about the context of those major totals? Federer is the all-time men's leader, three ahead of Nadal and Pete Sampras. Serena still trails Margaret Court (24), Steffi Graf (22), Helen Wills Moody (19) and Chris Evert and Martina Navratilova (18).
In some minds, degree of difficulty counts as well. Serena's rise from those public courts in Compton, California, is one of the most unlikely stories in the history of tennis.
Ultimately, there are still a few matches to play. Their legacies will be colored by how strong they finish -- and, perhaps, the circumstances under which they finish. They both have an opportunity to burnish their body of work in the next several days. So, the question will persist:
Federer or Serena -- who's had the more marvelous career?
It's a fair question.