US Open semi-finalist Frances Tiafoe said he was "flying high on confidence" after beating Yasutaka Uchiyama 6-3, 6-4 in the first round of the Japan Open on Monday.

The American made a name for himself when he stunned Rafael Nadal on his way to a shock final-four appearance at Flushing Meadows last month before playing a starring role at the Laver Cup.

The world number 19 is playing his first singles tournament since the US Open this week in Tokyo and he dispatched Japanese wild card Uchiyama with little fuss.

Tiafoe said he was "not really feeling any pressure" despite his recent achievements putting him firmly in the spotlight.

"Every day is different, guys may play well and they may beat you -- you've got to live with it," he said.

"I'm flying high on confidence and I'm just staying with my process."

Tiafoe will play Bernabe Zapata Miralles in the second round after the Spaniard beat Japan's Taro Daniel 7-5, 7-5.

Tiafoe did not lose a single service game against Uchiyama and closed the match out in 1hr, 12min.

"I hit the ball well from the ground, I moved well, made first serves when I needed them," he said.

"It was straight sets, I didn't get broken -- it could be worse."

Spain's Pedro Martinez also advanced to the second round with a 7-5, 6-4 win over Australia's Alexei Popyrin, while American Brandon Nakashima beat Japan's Shintaro Mochizuki 6-3, 6-2.

Norwegian top seed Casper Ruud will play Spain's Jaume Munar in his opening game on Tuesday, while Australian Nick Kyrgios takes on Taiwan's Tseng Chun-hsin later in the day.