Challenger Vault Kei Nishikori Jan 23, 2018 In this edition of the Challenger Vault, Kei Nishikori reflects on his maiden ATP Challenger Tour title in Bermuda in 2008 and talks about how the circuit helped grow his game. Tags: 2018 Challenger Kei Nishikori Share 0 Share on Facebook Tweet Tweet on Twitter +1 +1 on Google Plus