Naomi Osaka came back from within two games of an Australian Open third-round exit to beat Taiwanese Hsieh Su-wei 5-7 6-4 6-1.
The Sixth seeded player Elina Svitolina also diced with danger in a 4-6 6-4 7-5 win over Chinese world number 40 Zhang Shuai.
Japanese fourth seed Osaka lost the first set and was a break down in the second.
But she broke back twice at the end of the second and won seven games in a row to take the advantage in the decider.
The 21-year-old will face 13th seed Anastasija Sevastova next after the Latvian’s 6-3 6-3 victory over Wang Qiang of China.
Svitolina, who delivered a drink to shattered opponent Zhang at the end of their draining three-hour encounter, takes on 17th seed Madison Keys next after the American beat Belgian 12th seed Elise Mertens 6-3 6-2.
Spain’s two-time Grand Slam champion Garbine Muguruza beat Swiss Timea Bacsinszky 7-6 (7-5) 6-2 and will face Czech seventh seed Karolina Pliskova next.
Pliskova overcame Italy’s Camila Giorgi 6-4 3-6 6-2.