Maria Sharapova struggled on at the Australian Open but Caroline Wozniacki suffered yet another early exit at a grand slam.
Denmark's former world number one Wozniacki was beaten 4-6 7-5 6-3 by fast-improving young Spaniard Garbine Muguruza in the third round.
It meant that for an eighth successive slam Wozniacki has gone out before the quarter-finals, and she has reached the second week just once in that time.
Wozniacki led in the second set, and she said: "Sometimes it happens, you just don't take your chances.
"I don't think I did anything particularly wrong. I thought she played some great tennis as well. It was just a bit unlucky."
Sharapova needed almost three and a half hours to see off Karin Knapp in extreme heat on Thursday, and she wobbled in the second set against Alize Cornet on Saturday before pulling through 6-1 7-6 (8/6).
The third seed was so unhappy with her lack of rhythm that she hit the practice courts straight after her match.
Sharapova said: "Everyone that played a long match in those conditions (on Thursday) is going to feel physically and emotionally tired, and that's the way it goes.
"You just have to find a way to get through it. That's what I did. It was quite tough in the end. She had a set point and she had a chance to level the match, which is something I probably wouldn't want to do, go into a third set.
"I was happy I was able to finish it in two."
Sharapova missed the last three months of 2013 with a shoulder problem, and she added: "I still feel like in certain situations I am a bit rusty and I'm not closing it out when I have to or maybe going for a little much or over-thinking it a bit.
"That will come. I'm not worried about that. As long as I feel like I'm doing the right things and I'm playing the way I want to play, if I'm making those types of errors, they are going to go in eventually."
Sharapova next plays 20th seed Dominika Cibulkova, who benefited from Carla Suarez Navarro's exhaustion after an epic match in the heat on Thursday to win 6-1 6-0.
Muguruza, meanwhile, faces fifth seed Agnieszka Radwanska, who has been making hard work of her draw and came through another three-set match against Anastasia Pavlyuchenkova.
Last year's semi-finalist Sloane Stephens is through to the fourth round of a fifth straight grand slam after beating Elina Svitolina 7-5 6-4.
Eighth seed Jelena Jankovic and 11th seed Simona Halep were also straight-sets winners and will play each other in the last 16.