US Open champion 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.
Sixth seed 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.
She received treatment on her shoulders and neck and looked uncomfortable at times against Zhang, who also had the trainer on for a back problem in the third set.
Having gone a break up in the sixth game of the first set, Svitolina then lost back-to-back service games to allow Zhang to serve out the set.
Zhang continued to put pressure on the Svitolina in the second set, failing to convert a break point in the seventh game.
But she then allowed the world number seven back into the match when she went 0-40 on her serve to hand Svitolina three set points, the third of which she converted with a forehand winner.
The match looked to be out of Svitolina’s reach when she went a double break down early in the third set but after a change of top she began to stage her comeback.
There were seven breaks of serve in a gripping deciding set with Svitolina finally sealing victory on her second match point on Zhang’s serve.
“It was a very tough match for both of us,” Svitolina said. “She played unbelievable tennis and hopefully we’ll see many more of her talents back in Melbourne. It was very hot conditions so I was struggling a little.
“We left everything on court but we practise every day for those matches. I thought I will either die or win.
“I had to stay mentally strong. I was trying to stay out there as long as possible.”
But she was not her usual bubbly self on Margaret Court Arena in a nervy encounter in which she made 42 unforced errors.
She showed signs of frustration in the third game and slammed the ball into the court after being broken for the first time in the tournament midway through the opening set.
Osaka appeared to compose herself – breaking back immediately before moving 5-4 ahead.
But Hsieh went on to win six games in a row and Osaka’s frustrations grew as she threw her racquet into the ground following another break of serve.
Osaka began to bounce back at 4-1 down in the second set and she flipped the match on its head as she then went on to win seven consecutive games.
The 21-year-old dominated the third set – converting three of her five break points – and ensured she reached the last 16 for the second year in a row in Melbourne.
“I just didn’t want to give up,” said Osaka.
“I really love Grand Slams so I did anything I could do to stay here a bit longer”