Yuichi Sugita climbed to a personal-best 36th in the world rankings released Monday, while Kei Nishikori, who is out for the season with a right-wrist injury, remained in 14th.
Sugita, 29, reached the Japan Open quarterfinals last week to improve his ranking.
Nishikori, who has been out since mid-August, has stood at 14th since Sept. 11. He is scheduled to play at the New York Open and the Mexico Open in February.
Rafael Nadal stayed atop the rankings, while Roger Federer was second and Andy Murray third.