Djokovic will play fifth seed Nishikori in his semifinal after topping his group with three wins .
Djokovic can reclaim the No. 1 ranking by winning the tournament for the fifth successive year .
Djokovic , who can reclaim the No. 1 ranking by winning the tournament for the fifth successive year , will play fifth seed Nishikori in his semifinal after topping his group with three wins .