Novak Djokovic and Andy Murray have been rivals for years. But this year, their rivalry is probably at its peak as they battle for the ATP Men's Singles No. 1 at the Barclays ATP World Tour Finals in London.

The two rivals are in the semifinals after both players went 3-0 on their respective group bracket.

Novak Djokovic defeated Dominic Thiem, Milo Raonic and David Goffin in his group bracket to stay in contention for ATP Men's Singles No. 1. Andy Murray, on the other hand, beat Marin Cilic, Kei Nishikori and Stan Wawrinka in his group bracket.

On paper, Andy Murray has a 450-point lead over Novak Djokovic. Murray has 11,185 points while Djokovic has 10,780 points. But Murray's 275 points that he earned in the 2015 Davis Cup Finals will be gone on November 28, per ATP World Tour.

In the ATP World Tour Finals, a player earns 200 points for each round robin match win, 400 in the semi-finals and 500 in the finals.

With both players staying perfect at 3-0 on their respective brackets, each player earned 600 points. If either Murray or Djokovic lose to their semifinals match on Saturday at O2 Arena, the one who remains will clichéd this year's ATP Men's Singles No. 1. If both players lose to their respective semifinals matches, Murray will be the winner.

But if both players take care of business and succeed in their respective semifinals match, they will meet at the ATP Barclays World Tour Finals. If that happens, both elite players will not only fight for the ATP World Tour Finals trophy but for the top rank in ATP Men's Singles.

Murray is trying to become the 17th man (since 1973) to end up as No. 1. Djokovic, on the other hand, will try finish at the top of the ATP Men's Singles ranking for three consecutive years and fifth overall.

As further discussed by ATP World Tour, the last time that the No. 2 overtook the No. 1 ranked player at the ATP World Tour Finals happened in 2001 when Lleyton Hewitt of Australia outranked Gustavo Kuerten of Brazil.

It never happened in the history that the last match of the ATP World Tour determined the year-end No. 1. Could this be the first time that it will happen? Will the Andy Murray meet Novak Djokovic at the final match of the season finale to clash for 2016 year-end No. 1?

Murray is set to juggle with a semifinals match against Milo Raonic on Saturday at 14:00 GMT while Djokovic will battle with Kei Nishikori at 20:00 GMT, per BBC.