We knew Novak Djokovic had game the moment he reached the quarters of the 2006 Roland Garros, despite being only 19. All the pieces – serve, groundstrokes, movement, comfort on all surfaces – seemed to be there.

But we began to think of him as a future champion the next year, as he won his first pair of Masters shields, reached the semis of the RG and Wimbledon back to back, then got to the finals of the US Open. In the process, he scored victories over everyone that mattered, be it Roger Federer and Rafael Nadal to the up and coming Andy Murray.

The 2008 Australian Open, his first major title, was a coronation of sorts. In an ATP promotional video that spring, he said that the mentally strongest players on tour were “Federer, Nadal, and me.” As they were the only men to have won majors since early 2005, this didn’t seem like hyperbole.

We’re accustomed to seeing players who have mental strength from the get-go – Nadal, Lleyton Hewitt and Jimmy Connors come to mind – or who acquire it after they adapt to the predatory realities of the tour – Federer, Pete Sampras and Ivan Lendl were all made competitors, not born.

As for Djokovic, he’s a bit harder to classify. In each of his major runs in 2007, he fought off a five-set challenge early on, raising his game as the event progressed. In 2008 he won only four titles, but they were the AO, the Masters shields of Miami and Rome, and finally the Masters Cup in China to end the season. Many a great talent, from Thomas Enqvist to Henri Leconte, has not played his best in the majors, but Djokovic appeared to be the opposite.

The closest comparison that comes to mind is Boris Becker, who won his first major at age 17, added four more by 1991, and then reached No. 1 in the world that year. Following his upset defeat in the finals of Wimbledon that year, Becker became a far less consistent performer in the years to come, taking all of four years to start consistently contending for majors not played on grass, and four and half to win his sixth.

The Serb’s decline may be less precipitous than Becker’s, but ultimately it hurts more: Many of us who have appreciated his play are now aghast by his results, and wonder if he’ll ever reach the potential he once showed. There have been questions about his change of rackets, coaching issues, and health concerns, but the greatest regression has been mental.

After being beaten by Nadal at the 2008 RG semis, he didn’t show up at Wimbledon and was ushered out early by Marat Safin. After falling just short in a brutal battle with Nadal in Madrid last year, he sleepwalked into Paris and fell early.

(Of course, Nadal hasn’t been the same since then either; if he never wins a major Djokovic can say that he finished the Spaniard as a top player, though that’s probably not the distinction he was hoping for.)

In this past fall he had given hope to his many fans by going on a tear, winning three of four events at one stage and, once again, scoring wins over Nadal and Federer in the process. All a proper set up to a return to Australian Open glory … or so it seemed.

Djokovic played a fine event up to the quarters, where he ran into the streaky offensive player Jo-Wilfried Tsonga. Federer awaited the winner, having just hit his stride in dispatching Nikolay Davydenko, the hottest player on tour.

When Djokovic ran out to a 5-2 lead over Tsonga, it appeared that he might be playing well enough to test the Great Swiss. It was not to be: Kept off-balance by Tsonga’s power and unsure of how aggressive to be, Djokovic blew his lead and lost the first set in a tiebreak. A similar situation took place in the second set, but the Serb survived that breaker, running away with set three.

In set four, though, his physical ailments returned, and he could not close out the streaky Frenchman. He won just four games in the last two sets.

Instead of a Fed-Djoker semi, a clash between to of the most complete, natural-looking players on tour, we watched as Federer dissected Tsonga’s unsubtle game in straight sets, in much the way Djokovic should have.

The Serb’s physical frailty is certainly a concern, as the Tsonga match revealed. But if it weren’t for his mental frailty – the early leads he let slip away – his body might not have been given a chance to betray him.

Now, one can only wonder if Djokovic’s early momentum is gone for good. In the early part of his career he looked the part of a player tough enough to win the big ones. Now, it’s unclear whether he can handle adversity.

If he doesn’t, a potentially great career will go down as a great disappointment.