Top seed Serena Williams fought back from a set down in consecutive matches, seeing off 24th seed Garbine Muguruza in the Australian Open fourth round.

After being pushed to three sets by Elina Svitolina two days earlier, Williams was once again under pressure before prevailing 2-6 6-3 6-2 in two hours on Rod Laver Arena.

Muguruza ultimately could not keep up her stellar serving performance, and a dip in her first-service percentage - combined with an improvement from Williams' - in the third set helped the American get the decisive breaks late.

Williams finished with 41 winners to Muguruza's 29, while they both hit 35 unforced errors for the encounter.

A mammoth sixth game was the first small win for Muguruza, negotiating three break points in an 18-point affair to hold for a 4-2 lead in the first set.

And she rode the momentum into the next two games - Muguruza remarkably landing all eight first serves as she held to claim the opener.

Williams looked to fight back into the match when she broke for a 2-0 lead in the second set.

But her Spanish opponent was unflustered, with Muguruza levelling at 2-2 after saving two more break points, both thanks to her serve.

Muguruza's serve, including her second ball, was able to not only negate Williams - it made the American's serve look mild at times.

Normally Williams' way in against inferior opponents, Muguruza's second serve was instead winning her points more often than not - and denying the world number one a direct chance to dominate rallies.

But Muguruza did blink eventually - dropping serve in the eighth game of the set, and Williams went on to hold emphatically and force a decider.

Similarly to the sixth game of the first set, Muguruza fended off three more chances for Williams to break early in the third - surviving to win a 14-point game to edge ahead.

But Williams responded in kind - saving six break points in an eight-deuce second game, and it proved to be the match-changer.

The 18-time major winner then broke for a 2-1 lead, effectively ending Muguruza's resistance.

Williams won six of the final seven games to book a last-eight clash with 11th seed Dominika Cibulkova.