Nadal will replace Novak Djokovic as number one if he reaches the final, or the Serb fails to win the title.
The 27-year-old Spaniard won 6-4 7-6 (7-3) to set up a quarter-final against Italy's Fabio Fognini in Beijing.
It may be recalled that Nadal beat Kohlschreiber on his way to victory at the US Open last month. But it was a hard win as the match lasted four sets in New York, and the German tested him once again at China's National Tennis Centre.
