Third seed Gauff had taken apart 2021 US Open runner-up Fernandez in their only previous meeting at the United Cup mixed team tournament in late December and fans hoping for a tighter clash at Margaret Court Arena were left disappointed.
"I think it's harder (to face Fernandez again), because she knows what to expect. She played differently than she did at the United Cup," Gauff said.
"It's also harder because you're trying to change up from the last time. She's a great competitor and a great person, so I knew it would be a tough match regardless."
Having squandered three opportunities to break in a tough third game, Gauff pounced for a 4-3 advantage as Fernandez sent a shot long before the American dictated play to close out the opening set.
The gulf in class became even more evident as Gauff raced to a 3-0 lead in the second set and she pulled away to win her 16th successive set since the start of 2025 and advance in style at Melbourne Park.
The 2023 US Open champion will face Tokyo Olympics gold medallist Belinda Bencic in the next round after the Swiss went through when Naomi Osaka retired with an abdominal injury while trailing 7-6(3).