The 19-year-old Tsitsipas is coming off his first run to the fourth round at a Grand Slam tournament, last month at Wimbledon.
In the other half of the draw, three-time major champion Andy Murray pulled out of his quarterfinal after winning a trio of three-setters and lamenting a schedule that had him start his latest victory at midnight ET.
Murray cited fatigue when he withdrew Friday, hours before he was supposed to face 19-year-old Alex de Minaur, who was given a walkover into the semifinals of the hard-court tuneup for the US Open.
Murray’s third-round victory over Marius Copil ended just past 3 a.m. on Friday. Afterward, Murray told a small group of reporters that he “potentially” could withdraw from the tournament.
He also announced Friday that he was going to skip next week’s Toronto Masters.
Murray is working his way back into form after having surgery on his right hip and being sidelined for 11 months.