The fourth-seeded Tiafoe faces unseeded Kwon Soon-woo of South Korea in the last four on Saturday in Tokyo.
The American, who beat Rafael Nadal at the US Open on the way to his first Grand Slam semi-final, said he had been "solid from the start" of the 71-minute quarter-final.
"Great tennis today," he said. "I was moving really well, I hit the ball really well from the back of the court."
Tiafoe, the world number 19, said he had been struggling to adapt to the Tokyo time zone.
"I've been really bad and jet-lagged, so I've probably been sleeping pretty early and waking up really early," he said.
Kwon beat Spain's Pedro Martinez 6-3, 6-0, and Tiafoe said it would be "cool" to play the South Korean - who he faced at the Tokyo Olympics.
"Kwon's a great player. He's been playing really well this week, so it's going to be cool to play him, we practise sometimes in Florida."
The winner could be on their way to a potential clash with mercurial Australian star Nick Kyrgios, who plays third-seeded American Taylor Fritz later on Friday.
Tiafoe has been in the spotlight since stunning Nadal at Flushing Meadows and playing a starring role at the Laver Cup in London, where his Rest of the World Team beat Europe for the first time in the competition's history.
He has said he hopes to inspire a new generation of Black tennis players.
