MIAMI (AFP) - China's Li Na reached the quarter-finals of the Miami Masters here on Monday with an error strewn 7-6 (8/6), 6-2 win over giantkilling Spanish teenager Garbine Muguruza.

Li - who is playing in her first tournament since suffering an ankle injury in January's Australian Open - made 39 unforced errors including four double faults and allowed her 19-year-old opponent to battle back to 5-5 in the first set having led 5-1.

Even at 6-1 in the tiebreker Li faltered as 73rd-ranked Mugurza, who had claimed the scalps of the seeded Caroline Wozniacki and Anastasia Pavlyuchenkova in previous rounds, fought back to 6-6.

However, fifth-seeded Li pulled herself together to take the next two points and the set.

Li was more clinical in the second set breaking Mugurza, who was born in Venezuela but has a Spanish father who now lives in Barcelona, in the second game and closing the match out when her opponent served a double fault on match point.

Li will play top seed Serena Williams in the quarter-finals after the American came back from a set down to win 2-6, 6-4, 6-2 against Slovakia's 13th seed Dominika Cibulkova.