The rising Czech captured her third win over a top 5 player this season, and her 10th top 5 win in her career overall, with victory over reigning Australian Open champion Osaka in one hour and 49 minutes.
Muchova looked in fine form against Osaka as she survived a second-set comeback by the No.2 seed. The Czech had had 29 winners, two more than Osaka, and converted half of her eight break points on the day.
Osaka faltered early, double faulting down break point to cede a 2-1 lead to Muchova in the first set. The Japanese could not recover that break, and Muchova eased to a one-set lead.
Muchova took control early in the second set too, breaking for another 2-1 lead with continued aggression.
However, Osaka was up to the task this time, increasing the intensity of her forehand and earning her first break of the day to level at 3-3.
Osaka knocked off five games in a row to sweep through the rest of the set and tie up the match at one set apiece as Muchova’s first-service percentage dropped from 73 per cent in the opener to 52 per cent in the second set.
In the decider, though, Muchova got back on track. At 1-0, the Czech fired a passing winner to set up break point, then used a deep return to earn an early break. Muchova was untroubled the rest of the way, zipping home to notch her 10th match-win of the season and claim her spot in the Madrid Round of 16.