Rafael Nadal will finish the year as the top-ranked male tennis player for the fourth time.
The 31-year-old Spaniard assured himself the world No.1 ranking by beating Hyeon Chung 7-5 6-3 in the second round of the Paris Masters.
The 16-time grand slam winner had not finished the year at the top since 2013, with Novak Djokovic and Andy Murray doing so after that.
"One year ago, for sure I never dreamed about being No.1 again at the end of the season," Nadal said.
Nadal's comeback from injury, loss of form and confidence, has been remarkable.
He reached three grand slam finals this year, losing to Roger Federer at the Australian Open and winning a 10th French Open title before clinching the US Open for the third time.