Novak Djokovic's U.S Open title allowed him to clinch the year-end No. 1 ranking for the fourth time.
The ATP announced Monday, a day after Djokovic's 6-4, 5-7, 6-4, 6-4 victory over No. 2 Roger Federer in the final at Flushing Meadows, that the 28-year-old Serbian would add 2015 to 2011, 2012 and 2014 as seasons he finished atop the rankings.
"Knowing I will end the year at No. 1 keeps my mind relaxed," Djokovic said in an interview with The Associated Press. "I have achieved a lot so far in the season, and I hope I can deliver the same game for the rest of the year."
He is 63-5 with seven titles, including three at Grand Slam tournaments, and has...