Dimitrov, who used to be ranked third, is now ranked 78th after he had lost seven of eight matches heading into the US Open, including a straight-sets loss to No. 405 Kevin King in July at the Atlanta Open. He also lost in the first round of the Rogers Cup and the Western & Southern Open.
"I do think he was a better player in first set. I do think I was kind of lucky to win it," Medvedev said about Dimitrov. "Then the momentum changed completely. I think after, I was playing better than him in the next two sets."
Medvedev, 23, will take on the winner of Saturday night’s second semifinal, the 18-time major champion Rafael Nadal, after his victory over Italy’s Matteo Berrettini under the roof at Arthur Ashe Stadium on Friday night immediately following Medvedev’s match.