Nadal is seeking his fifth time as the year-end No. 1. (Getty Images)

With only a few weeks left in the ATP season, the battle for year-end No. 1 is heating up just as the weather is starting to cool. Only two players have a chance at finishing the season with the coveted top ranking: Rafael Nadal and Novak Djokovic.

Currently, the Serbian holds the No. 1 ranking, but Nadal is only 320 points behind. If Nadal can win this week, at a tournament he's never won, he'll claim the year-end spot from Djokovic. If Djokovic wins Paris, the race continues in London. There are 1,000 points to play for in Paris and 1,500 in London.

Both players are currently in the semifinals.