Novak Djokovic clinched the year-end No. 1 ranking on Friday, according to the Associated Press.
It is the third time in four years that Djokovic will finish the year ranked No. 1 in the world, and he becomes the seventh man to finish No. 1 three different times.
Djokovic clinched the ranking with a win over Tomas Berdych in the ATP World Tour Finals, giving him a lead that second-ranked Roger Federer cannot overcome.
"It's an incredible achievement. Being No. 1 in the world is one of the biggest challenges a tennis player can have," he said. "I've been playing since I was four. I was very fortunate to have very knowledgeable people, people who believed in me, and believed in my talent."
In 2014, Djokovic won Wimbledon after defeating Federer in the finals, which was when he returned to the No. 1 ranking over Rafael Nadal. Djokovic also reached the final of the French Open and the semifinals of the U.S. Open this year, and won the China Open.
Djokovic plays Kei Nishikori in the semifinals on Saturday.
- Molly Geary