Dane Wozniacki, seeded 10th, appeared to be on course for a sixth appearance in the fourth round in seven visits to Melbourne Park when she wrapped up the first set in 39 minutes. Venezuela-born Muguruza, however, arrived in Melbourne in good form after winning the warm-up tournament in Hobart as a qualifier and rallied to clinch the second set in just under an hour on Rod Laver Arena.
With both serves under pressure in the decider, the 20-year-old Spaniard converted all four of her break points to reach the fourth round of a grand slam for the first time. Muguruza next meets fifth seed Agnieszka Radwanska of Poland.
(Reporting by Nick Mulvenney; Editing by John O'Brien)