Ben Shelton is confident he can retain his Japan Open crown after kickstarting his title defence with a victory over fellow American Reilly Opelka in three sets. 

Shelton, who captured his maiden tour-level trophy a year ago in Tokyo, came from a set down to win 3-6 6-1 6-4 in an hour and 47 minutes on Thursday. 

He came into the competition off the back of a victory over Daniil Medvedev at the Laver Cup, though Team World went on to lose the tournament in Berlin. 

However, with consecutive wins under his belt, the 21-year-old American believes his previous success in Tokyo will stand him in good stead this time around. 

"I have a lot of love for this tournament and this city," Shelton said. "I have a lot of confidence. Being here and knowing the situations I have come through in this exact stadium, in the most important moments."

"I think it was a tough start. I felt like I was struggling a little bit and getting rhythm. I am happy with the way I competed. Breaking serve multiple times gives me a lot of confidence."

Former Japan Open champion Taylor Fritz, though, suffered a shock first-round exit in three sets to Frenchman Arthur Fils. 

Fils produced a classy performance on his tournament debut in Tokyo, handing the recent US Open finalist a 6-4 6-3 6-3 defeat.

Stefanos Tsitsipas was another big name to suffer a shock defeat, as he lost 4-6 6-1 6-2 to Alex Michelsen.

Holger Rune, however, booked his place in the next round, but was pushed all the way by Alejandro Tabilo, eventually prevailing 6-2 5-7 6-4 in the decider. 

Up next for the Dane is wildcard Yoshihito Nishioka.