Kei Nishikori has said that successfully defending his title at the US National Indoor Championships gave him "an amazing feeling".
The 24-year-old retained his crown by beating Croatia's Ivo Karlovic 6-4 7-6 in Sunday's final.
"It's an amazing feeling," Nishikori told reporters. "I had never defended a title before."
Nishikori has now won four ATP World Tour titles. As well as claiming back-to-back trophies in Memphis, the Japanese number one triumphed at Delray Beach in 2008 and in Tokyo in 2012.
