Novak Djokovic is the No. 1 tennis player in the world, thanks in large part to a truly outstanding 2011 season.
But, even though he's the defending champion in the Australian Open, he won't win the tournament this year.
That's because he's facing more difficult competition in 2012.
If he meets one of those two in the finals, which he almost certainly will if he advances that far, both of those players have beaten Djokovic more than they've lost to him.
Nadal is 16-13 against the Djoker, though Djokovic has a 10-5 advantage on hard courts. However, anything can happen when two greats meet, and Nadal is one of a select few people who can actually beat Djokovic on hard courts.
Meanwhile, against Federer, Djokovic is even worse. Federer leads their all-time series 14-10.
In fact, when Djokovic was off to a hot start in 2011, winning his first 41 matches, it was Federer who ended the streak in the French Open semifinals.
If Federer can advance to the finals and play Djokovic, he's healthy enough to make sure it's similar to the results Federer used to enjoy against Djokovic in the US Open.
But, let's not get ahead of ourselves. Before Djokovic can play Federer or Nadal in the finals, he has to actually make it to the finals.
Who presents the biggest challenge for Novak Djokovic?
To do that, he'll most likely have to beat either No. 4 Andy Murray or No. 5 David Ferrer.
If there's one player who's equal to Djokovic on hard courts, it's Murray, who is 4-4 against Djokovic when they meet on hard courts.
Though Djokovic won the 2011 Australian Open against Murray, Murray is 3-1 in finals against the Serbian.
If they meet in the semifinals, Murray will give Djokovic everything he can handle. And, even if Djoker wins, he'll be exhausted for the finals.
Then, either Nadal or Federer will make their move and claim the 2012 Australian Open.
Djokovic had a great 2011, but 2012 is going to be the year of Nadal and Federer's returns to dominance.
Expect Djokovic to fall to No. 3 by the end of this season and don't be surprised if he doesn't win a Grand Slam event this year.