One Record Djokovic May Not Match

Can Novak Djokovic craft the best season in tennis history?

In June, Djokovic lost to Roger Federer in the French Open semifinals, falling just one win short of tying John McEnroe's record start to a season of 42-0 in 1984. Since then, Djokovic has won Wimbledon and the Masters event in Montreal, winning 12 straight matches and dropping just five sets.

Entering Thursday's last-16 match against Radek Stepanek at the Cincinnati Masters, that left him with a remarkable winning percentage of 98.2%, better than McEnroe's season-ending percentage of 96.5% in 1984.

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Novak Djokovic, playing this week in Ohio, is winning at a better rate so far this year than John McEnroe did in his remarkable 1984 season.

"Every match I play, I try to win, regardless of which match it is or whoever is across the net," Djokovic said Sunday after winning his ninth tournament of the season in Montreal.

But does that mean that Djokovic is a good bet to exceed McEnroe's season record of 82-3? Not really—unless you believe that Djokovic this year has transcended to a new level of dominance that can't be captured by the ordinary laws of probability, which is a defensible position.

First, the cold numbers. Assuming he stays healthy and motivated, Djokovic is likely to play at least five more tournaments: the Masters that began this week in Cincinnati, the U.S. Open, Masters tournaments in the fall in Shanghai and Paris, and the year-end tour finals in London. Each one should feature most if not all of the world's top male players. But there's another variable that will make it harder for Djokovic to match McEnroe's mark: His Serbian team is in the Davis Cup semifinals, which means he could play as many as four more singles matches in that competition, three of them against top-caliber opponents.

It's difficult to say for sure what Djokovic's chances are of winning in each event: Final entry lists aren't yet available, let alone draws. But even for a player as good as Djokovic, a sophisticated probability model gives him less than a one-third chance of winning an event featuring all of his top peers. Jeff Sackmann, a tennis-stats blogger at Heavy Topspin, has developed a ranking and forecasting algorithm that gives Djokovic a 29.6% chance of winning in Cincinnati this week.

Sackmann also forecast Djokovic's chance of having won Wimbledon at about 25%. Apply that to the U.S. Open, and Djokovic's Cincy chances to Shanghai and Paris, and he has less than a 1% chance of sweeping the three Masters and the U.S. Open, compared to a 26% chance of falling short in all four events, which means he'd take on four more losses, already two more than McEnroe.

The tour final is a bit different, because a player can win it all yet emerge with a round-robin loss—or even lose three matches, by getting swept in the round-robin phase or by advancing to the knockout stage with two losses and then getting knocked out. Djokovic is the current heavy favorite in that tournament, yet Sackmann, based on the current likely tour finalists, gives Djokovic just a 17% chance of winning it undefeated—and a 4% chance of losing three matches.

Davis Cup is even tougher to forecast, because final team lineups aren't set and because Djokovic, even if he does play Serbia's semifinal against Argentina, could play anywhere from one to four singles matches between now and the end of the year. Still, even with a favorable schedule, Djokovic has a 40% chance of taking at least one loss in Davis Cup play.

This all adds up to less than a 1% chance Djokovic loses no more than one more match this season, to better McEnroe's feat; about a 5% chance he'll lose exactly twice and match McEnroe, and an 84% chance he'll lose three matches or more.

"It's really, really difficult what he's doing," said Rafael Nadal, who surrendered his world No.1 ranking to Djokovic in May. "He's having a better season than I had in 2008. Just congratulate him."

Still, Djokovic has a chance to match or exceed McEnroe in respects other than won-loss record, which is, after all, rarely considered the determinant of tennis greatness. If he wins the U.S. Open, the tour finals and Davis Cup, he'll have matched McEnroe in majors and tour finals while one-upping him in Davis Cup, where McEnroe's U.S. team lost to Sweden in the finals in part because he lost his opening singles match in straight sets.

In some respects, Djokovic has already exceeded Federer's 2005 season, in which he finished 81-4 after going two sets up in his final match with a chance to equal McEnroe's record before losing three straight sets to David Nalbandian. Federer reached just two major finals that year, winning them both, which Djokovic already has matched heading into the U.S. Open. Federer also entered just five of the nine Masters events, winning four and losing in Monte Carlo in the quarterfinals; Cincinnati is Djokovic's sixth, and he's already won five, a record total.

Federer was also 15-2 against Top-10 opponents that year, while Djokovic is 16-1, meaning he's already won more against top competition than Federer did, with many big tournaments left to play.

"He's as good an athlete as we have out here," said Mardy Fish following his defeat by Djokovic in the Montreal final last weekend. "He gets to balls, just his racquet on balls that you can't believe he gets to."

Even if Djokovic's chances of beating McEnroe's 82-3 mark appear remote, there are some important caveats: First, he's defied probability already this season with his improbable run, and hasn't needed a lot of luck in most of his wins. Just nine have gone to a deciding set, and in just four of those was the deciding set close.

He could also catch some lucky breaks along the way: Some top players might skip Paris; or potential opponents on rival Davis Cup teams might get injured or skip the tournament. Djokovic can even help himself by skipping one of the later Masters tournament—particularly if he's won the U.S. Open by then, since he'll have little to prove.

Whatever happens, he'll have the world's best players gunning for him, but they have been all season and have consistently fallen short. "I'm aware of the fantastic year that I had and a great streak, but I'm not thinking how many matches will I lose," Djokovic said. "I'm thinking how many matches will I win. As long as it's like that, I think I'm in the right direction."

Write to Carl Bialik at numbersguy@wsj.com

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