PARIS — One of them focuses on numbers, hoping they will produce the validation he has always craved. Another one has come to play on the court that turns him into an apotheosis of his sport, and to protect this place as his personal kingdom. The third yearns for whatever there is left, and prepares for what comes next. The Big Three on the men's side of tennis — Novak Djokovic, Rafael Nadal and Roger Federer — are playing in a Grand Slam event for the first time in 18 months. Through a quirk in the sport's seeding system, they are all in the same half of the draw. Djokovic could face Federer in a quarterfinal and Nadal in a semifinal. They are not getting any younger. Djokovic and Nadal are 34 and Federer, at 39, is sputtering through his comeback from knee surgery. There may only be a few more Slams like this one. For years, they have been blessed with ethereal tennis gifts, so formidable for so long that opponents can feel that they are down a set even before the first point is played. It has been hard for slighter players to imagine beating them, let alone actually doing so. They still love to compete, really love to win (though Federer has won just once all year), and embrace the global celebrity that comes with being a tennis superstar. Any debate about who will end his career with the most Grand Slam singles titles and have a rightful claim to being the greatest quickly becomes reductive. They diverge dramatically, however, when the conversation shifts to what drives each of them to continue playing long after they have made hundreds of millions of dollars and solidified their reputations for history. And these thirty-somethings are well past the sell-by date of the great players of every era that preceded them. But at this singular moment in their careers, with Federer and Nadal tied at 20 Grand Slam wins and Djokovic close behind with 18, only Djokovic is so intently focused on the numbers. Djokovic, who just celebrated his 34th birthday and in the eyes of most experts is the most likely to finish on top, leaves no doubt that the chase for scoreboard supremacy motivates him."Whether I think about winning more Slams and breaking records, of course, of course, I do," Djokovic said in February, after beating Daniil Medvedev in the Australian Open final.