Maria Sharapova's struggles caught up with her as she followed Serena Williams out of the Australian Open.
The third seed had spent two minutes short of seven hours on court in her first three matches, half of it in extreme heat in the second round against Karin Knapp.
All appeared well when she won the first set of her fourth-round match against Dominika Cibulkova but Sharapova needed treatment for a hip problem and faded to a 3-6 6-4 6-1 defeat.
The Russian missed the latter part of last season with a shoulder problem, and she said: "Those aches and pains are expected when you spend a long time on the court. You just have to play through it.
"This is only my second tournament back, so it was those types of things that are expected.
"I haven't been playing the best tennis of this tournament, but I found ways to get through the last two matches. I tried to do that again today, but she played extremely well.
"I have to look at the positives and see where I have come from in four or five months. I haven't played a lot of tennis in those six months.
"I certainly would have loved to play a little bit more before playing a grand slam, but this is the chance that I was given.
"I'm smart enough to be able to take it and acknowledge that I'm still pretty lucky to be in the draw and giving myself a chance to try to win it."
Cibulkova, who at 5ft 3in was giving away almost a foot in height, completed her set of grand slam quarter-finals.
The Slovakian, who hammered Sharapova at the French Open in 2009, said: "This is what I'm really, really happy for, finally I made it.
"I showed that I had a great pre-season in December so it feels amazing.
"I went on the court and I was more than 100 per cent sure that I really could beat her. I could beat her on the big court, in an important match, at a grand slam.
"I did it before, and I knew she knows me. I also knew that she knows it's going to be a tough match. I was prepared for it."
Cibulkova next meets Romania's Simona Halep, who reached her first grand slam quarter-final with a 6-4 2-6 6-0 win over eighth seed Jelena Jankovic.
Halep won six titles last season, more than anyone except Williams, and will break into the top 10 at the end of this tournament.
The exits of Sharapova and Williams - beaten by Ana Ivanovic on Sunday - left second seed Victoria Azarenka as the clear favourite to win her third straight Australian Open title.
Azarenka was taking on Sloane Stephens in a rematch of last year's controversial semi-final, when the Belarusian indicated she had taken a medical time-out late in the match for tactical reasons.
She later insisted there had been a misunderstanding but the damage was done and, asked about their off-court relationship prior to the match, Stephens simply replied: "Non-existent."
There was nothing too controversial this time, although Stephens did hit Azarenka with a shot - the champion responding by appearing to aim a volley at her opponent's head.
The main talking point, though, was how well Azarenka played in a clinical 6-3 6-2 victory.
The 24-year-old insisted her mindset would not change following the exits of her two biggest rivals, saying: "It doesn't matter.
"We still have high competition out there. The players who beat those players deserve all the credit because they've been better, so they are dangerous and they are competitive."
Azarenka also shrugged off being hit by Stephens, adding: "Maybe she had an open court, but she chose that shot. I have no problem with that."
The 20-year-old American, meanwhile, denied she had celebrated Williams' defeat on Sunday.
TV pictures appeared to show Stephens raising her arms aloft but she insisted she and British hitting partner Andrew Fitzpatrick were simply mimicking the excited reaction of Ivanovic's support team.
Stephens beat Williams in the quarter-finals in Melbourne last year and then did an interview in which she was critical of her countrywoman for subsequently snubbing her.
Both have insisted the issue is in the past, and Stephens said: "In reports and everything it became that I'm cheering against Serena, which had nothing to do with it. We were just having some fun."
In the quarter-finals, Azarenka will play fifth seed Agnieszka Radwanska, who defeated Spain's Garbine Muguruza 6-1 6-3 in the night session on Rod Laver Arena.
Azarenka has won their last seven meetings, with Radwanska's most recent set against the second seed coming in Melbourne two years ago.