
The 10th-seeded Czech, beaten in the final of this year’s French Open, overcame an error-strewn performance to win 6-3, 5-7, 6-1 in two hours 34 minutes at the Louis Armstrong Stadium.
The 27-year-old right-hander will face either Sorana Cirstea, the 30th seed from Romania or 15th-seeded Belinda Bencic of Switzerland in the last eight.
Wang had been bidding to reach the quarterfinals of a Grand Slam for the first time after an impressive run to the last 16 in New York.
The 21-year-old from Shenzhen fought back to level after taking the second set, but wilted in the decider as Muchova broke twice to take a grip on the match before holding to clinch victory.