Tomas Machac shocked Carlos Alcaraz to tee up a Shanghai Masters semi-final against Jannik Sinner. (More Tennis News)
Alcaraz beat Sinner to win the China Open title last week, and a rematch against the world number one looked on the cards with the Spaniard going up against the world number 33.
Yet Machac had other ideas and prevailed 7-6 (7-5) 7-5 on Thursday.
It brought up Machac's second win over a top-five opponent, after the Czech defeated Novak Djokovic at the Geneva Open earlier this year, only to lose to Casper Ruud in the final.
Reflecting on his win, Machac said: "I was playing unbelievable. I knew my level of tennis today would be great because I'm playing the best of my career right now for sure.
"I beat Tommy Paul [in the] last match with an unbelievable performance. With these kind of players, I have to play at this level. Otherwise, it's 6-2 6-3 and you go home. There's no other option.
"I knew that I had a chance [to beat Alcaraz], but you never know, even with a set and 5-4 it's still so far from winning the match. I played great tennis against him in the Davis Cup [in September], but there was this level [for] only one set. Today it was [for] two, so it was enough."
Data Debrief: Giant killers
From the round of 16 onwards, two players ranked outside the ATP's top 20 (David Goffin and Machac) have claimed top five wins at the Shanghai Masters for the first time in the event's history.
Since the inaugural event in 2009, meanwhile, Machac is now the fifth player ranked outside the ATP's top 30 to reach the last four at the Shanghai Masters after Feliciano Lopez, Juan Monaco, Kei Nishikori and Gilles Simon.
