Rafael Nadal struggled into his first Grand Slam quarter-final since 2015 at the Australian Open on Monday, as Serena Williams accelerated towards a record title and the number one ranking.
Nadal, searching for a revival after an injury-wrecked 2016 season, was tested by France's Gael Monfils before winning 6-3, 6-3, 4-6, 6-4 to book a last-eight clash with Milos Raonic.
Nadal, 30, was also pushed to five sets by Alexander Zverev, 19, in round three, but he has survived to reach his first major quarter-final since the 2015 French Open.
The Spanish World No.9 now has an excellent chance to add to his 14 Grand Slam titles after world number one Andy Murray and title-holder Novak Djokovic were both knocked out.
"I'm very happy being in the quarter-finals of a Grand Slam after a couple of years without being there," he said.
"It's very special for me, especially here in Australia where I feel (it's) a little bit like home."
A day after defending women's champion and top seed Angelique Kerber also fell by the wayside, Williams beat Barbora Strycova 7-5, 6-4 to set up a last-eight meeting with Johanna Konta.
The American great would gain much from winning in Melbourne, as she would overtake Steffi Graf's Open-era record of 22 Grand Slam titles and end Kerber's short reign as world number one.
In hot afternoon conditions, she fought off the Czech Republic's Strycova in two tight sets, following her sister Venus into the quarter-finals without dropping a set.
"I have absolutely nothing to lose in this tournament," said Williams, 35. "Everything here is a bonus for me.
Obviously I'm here to win. Hopefully I can play better, I can only go better."
Britain's Konta, the ninth seed, also reached the last eight with a perfect record in sets after a convincing 6-1, 6-4 victory over Russia's Ekaterina Makarova.
Despite the task facing her, Konta was delighted to be playing Williams, a childhood idol, for what would be her second straight Australian Open semi-final.
"I'm really looking forward to the challenge and I'm looking forward to being on court, out on court with her and competing against her," said the 25-year-old.
Mirjana Lucic-Baroni wrote another chapter in her fairytale career revival when she beat American qualifier Jennifer Brady 6-4, 6-2 to reach her first Grand Slam quarter-final in 18 years.
The former teen prodigy, now 34, won the 1998 Australian Open women's doubles with Martina Hingis but she fled her abusive father and suffered a series of injuries to put her career on hold.
Her joy was unbridled at beating Brady as she reached the last eight at a major for the first time since 1999, when she lost to Graf at Wimbledon aged 17.
"I hope no one is going to pinch me and wake me up because this is just incredible," said Lucic-Baroni, who screeched with joy and jumped up and down to celebrate the win.
"I am a tough little cookie and really stubborn: when I want something I will work hard and do anything I need to get it. What a satisfaction."
Lucic-Baroni will play her quarter-final against US Open finalist Karolina Pliskova, who ended home hopes with a 6-3, 6-3 win over Australia's Daria Gavrilova.
In the men's draw, David Goffin put away Austria's Dominic Thiem 5-7, 7-6 (7/4), 6-2, 6-2 to become the first Belgian man to reach the Australian quarter-finals.
Goffin will next play Grigor Dimitrov, who halted the fairytale run of Denis Istomin, the 117th-ranked Uzbek wildcard who shocked defending champion Novak Djokovic in round two.
The bespectacled Istomin won the first set but injury problems set in and he went down 2-6, 7-6 (7/2), 6-2, 6-1 to the in-form Bulgarian.
Canadian third seed Raonic, still suffering from the effects of flu, beat Spain's Roberto Bautista Agut 7-6 (8/6), 3-6, 6-4, 6-1 to earn his quarter-final against Nadal.