In 2015 , he has climbed as high as # 4 in the world rankings .
Nishikori became the first Asian player to reach a Grand Slam final in singles at the 2014 US Open .
In 2015 , Nishikori has climbed as high as # 4 in the world rankings .
Nishikori became the first Asian player to reach a Grand Slam final in singles at the 2014 US Open .