Japan's Kei Nishikori, who has secured a spot in the season-ending ATP Finals, jumped two places to No. 9 in the ATP rankings on Monday.Nishikori broke into the top 10 for the first time since August 2017, when he suffered a season-ending wrist injury. Paris Masters runner-up Novak Djokovic returned to No. 1 for the first time in two years.The 28-year-old Japanese qualified for the Nov. 11-18 season finale in London following the withdrawal of Argentina's Juan Martin del Potro due to a right knee injury. Nishikori and Djokovic are among the eight leading singles players to compete in the AT…READ FULL ARTICLE