The defending champion Fernandez saved all three break points in the 80-minute victory and will face ninth-seeded Bernarda Pera in the round of eight.
Two seeded players were knocked out, with Russia's Anastasia Zakharova eliminating seventh seed Varvara Gracheva of France 6-3, 6-1 and Suzan Lamens of the Netherlands outlasting eighth seed Cristina Bucsa of Spain 5-7, 6-4, 6-3.
Sofia Kenin advanced with a 7-5, 6-4 defeat of France's Jessika Ponchet.
Jiangxi Open
Second seed Rebecca Sramkova of Slovakia moved into the quarterfinals with a 7-5, 6-3 victory over China's Sijia Wei in Jiujiang, China.
Sramkova saved seven of 13 break points and took advantage of seven double faults by Wei to set up a match with Italy's Martina Trevisan, a 7-6, 6-2 winner against Anna Bondar of Hungary.
Sixth-seeded Dutchwoman Arantxa Rus defeated Czech Linda Fruhvirtova 6-4, 7-6 and Switzerland's Viktorija Golubic was leading 6-2 when fourth seed Jessica Bouzas Maneiro of Spain was forced to retire.