Using his explosive power and accuracy, second-seeded Sinner defeated his Czech opponent, rated 60th, 6-4, 6-2.
Machac advanced to the first Masters quarterfinal by defeating Andy Murray and Andrey Rublev, but Sinner’s skill level was too high.
The 22-year-old Italian will play Daniil Medvedev, the third seed, in a replay of the Australian Open final from January.
At Melbourne Park, Sinner defeated the Russian to win his first Grand Slam championship, and he has since maintained his excellent form.
After rising to the semifinals at Indian Wells, the world number three lost only to Carlos Alcaraz. He had already won another championship in Rotterdam.
Sinner and Alcaraz are developing a growing rivalry, and on Thursday, when the 20-year-old Spaniard takes on Grigor Dimitrov of Bulgaria in the last eight, they are still expected to face off in the Miami final.
Sinner overcame an early break of serve against the 23-year-old Machac and then settled into a rhythm to make it to the final four without any more significant issues.
