For much of 2018, it has a been a close battle for the world No. 1 ranking, as tennis legends Rafael Nadal and Roger Federer were separated by a slim margin. 

Not anymore.

Nadal has taken a commanding leading ahead of the U.S. Open, the final Grand Slam of the year. Nadal, who is competing in the final at the Rogers Cup on Sunday, has 9,310 ATP points compared to Federer's 7,080, for a difference of 2,230. 

Alexander Zverev, who has yet to capture a Grand Slam, is a distant third with 5,665. He is followed by No. 4 Juan Martin del Potro (5,455), No. 5 Grigor Dimitrov (4,610) and No. 6 Kevin Anderson (4,355).

Wimbledon champion Novak Djokovic continues to climb the rankings. The Serbian star, boasting 13 career Grand Slams on his resume, is ranked No. 10 with 3,355 points, trailing Nadal by 5,995 points and Federer by 3,725 points.

Nadal took home another French Open title this year and has a 35-3 record to go along with four tournament wins. Federer won the Australian Open but skipped the French, and has a 29-4 record with three titles in 2018. 

With a strong performance at Flushing Meadows, Federer can significantly cut into Nadal's lead. The Swiss star hasn't won the tournament since 2008 and was knocked out in the quarterfinals in 2017. He elected to skip the Rogers Cup in Toronto to prepare for the Cincinnati Masters and the U.S. Open.

Nadal is the defending U.S. Open champion, having defeated Dominic Thiem in the final, 6-4 6-3 6-2. It was a momentous achievement for the Spaniard on hardcourt after failing to reach the quarterfinals in his previous two U.S. Open runs.

Despite their well-documented rivalry, Nadal and Federer have not faced each other since October 2017, when Federer prevailed at the Shanghai Masters, 6-4 6-3.

The U.S. Open starts on Aug. 27.