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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.

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."