Kei Nishikori rose one spot in the world rankings released Monday by the ATP, moving up from seventh to sixth.
On Saturday, Nishikori lost his semifinal at the Rotterdam Open in three sets against Switzerland's Stan Wawrinka. The Japanese was seeking his second title of the season after winning the Brisbane International last month.
The world's top three remained unchanged, with Serbia's Novak Djokovic remaining at No. 1 followed by Spaniard Rafael Nadal and Germany's Alexander Zverev.
Elsewhere for Japan, Yoshihito Nishioka is ranked 72nd with compatriot Taro Daniel one spot behind in 73rd.