Novak Djokovic of Serbia wins the men's championship match against Rafael Nadal of Spain at the U.S. Open tennis tournament in New York, Monday, Sept. 12, 2011. (Charles Krupa/AP)

Of course, there’s little question that Djokovic’s raw physical game is tremendous. He has won three Grand Slam tournaments this season. In 2011, he’s had 64 wins and only two losses, a record many are already calling one of the best seasons in tennis history. Monday night, he broke Nadal’s serve an astounding 11 times

But it’s easy in the face of all that athleticism to forget the extraordinary power of a player’s psychological game, too. Nadal knew that. So did Djokovic, whose banner year gave him a mental leg up in the epic match that now ranks as the fifth longest men’s final in U.S. Open history. As ESPN’s Greg Garber put it, “Djokovic's confidence is currently the game's greatest weapon.”

It’s not as if Nadal didn’t bring his best game to the match. He may not have equaled Djokovic’s performance, but this was still tennis at its highest level. Nadal broke Djokovic’s serve several times himself. He had his opponent running all over the court. And he pulled off a stunning tiebreaker in the third set.

But Djokovic’s confidence was impenetrable. It had, after all, been on full display just two days before, when the Serbian tennis phenom hit a nervy gamble of a shot on match point in a stunning semifinal match against Roger Federer he went on to win. Of course, Federer wouldn’t call it that: “Confidence?” he replied to a questioner when asked if The Shot was illustrative of Djokovic’s grit. “Are you kidding me? I mean, please.”

Had Djokovic not gone on to beat Nadal in such stunning fashion, Federer might have been right. But Monday’s game proved that the same inner cool that led Djokovic to take that risky shot in the semis was the same fortitude that had him believing he was in control for every shot of that epic tournament win. As long as all that self-assurance is kept in check—that same boldness can also lead to too many risks and too little preparation—Djokovic’s performance is a reminder that at the highest level, physical power and raw talent are table stakes. It’s mental toughness that sets leading players apart.

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