Rafael Nadal has warned Novak Djokovic that his unbeaten start to 2011 won't last forever.

Djokovic beat Nadal 6-4, 6-4 in the Rome Masters final to deny the Spaniard a sixth title in seven years and take his winning streak to 37 matches this year.

It was the fourth time this season the Serbian has beaten the world No 1 in a Masters final and the second time on clay in the space of eight days after his Madrid triumph.

With the French Open beginning next Sunday, Nadal faces the prospect of not being the favorite, even though he has won there five times in six years.

But Nadal said he is focussing on improving his own game so that when the time comes, he will be the one ready to pounce.

"I'm there all the time, I've played in six straight finals, I've lost four (Miami, Indian Wells, Madrid and Rome; wins at Monte Carlo and Barcelona) but there is one player playing better than the rest, he is doing unbelievably," said Nadal.