Melbourne (AFP) - Rafael Nadal dug deep into his immense reserves of resilience for the second match running to keep his dream of a 21st Grand Slam title alive at the Australian Open on Tuesday, as unseeded American Madison Keys reached the women’s semi-finals.

Nadal raced to a two-set quarter-final lead against Denis Shapovalov but then began to feel unwell, needing medical attention for a stomach complaint before surviving a four-hour thriller 6-3, 6-4, 4-6, 3-6, 6-3.

The Spanish sixth seed previously had to show all his experience and tenacity just to reach the quarter-final in an epic 28-minute tiebreak, and he somehow found the willpower again to cross the finish line, despite being badly hampered.

“I started to feel not very well in my stomach so I just asked if they could do something,” said Nadal of calling for medical assistance.

“They just checked everything was all right and then I took some tablets to try to improve the situation. It was lucky that I was serving great in the fifth.”

Nadal won a warm-up tournament and continues to amaze even himself after being out for most of 2021 with a chronic foot injury. He then caught Covid-19 in December.

“I’m not 21 anymore!” he said.

“The real truth is that two months ago we didn’t know if we will be able to be back on tour at all,” Nadal admitted.

“It’s just a present of life that I am here playing tennis again.”

A frustrated Shapovalov smashed his racquet after losing and had a running battle with the chair umpire over the time Nadal was taking to serve, at one point calling the official “corrupt”.

- ‘Means a lot’ -

Earlier on Rod Laver Arena, Keys continued her impeccable start to the 2022 season with a straight-sets destruction of fourth seed Barbora Krejcikova to set up a potential women’s semi-final against Ashleigh Barty.

The unseeded world number 51 Keys was a semi-finalist in 2015 but endured a terrible 2021 where she tumbled down the rankings.

“It means a lot,” said Keys, who won 6-3, 6-2 against the French Open champion Krejcikova, who needed medical attention in the heat during the first set. “Last year was really hard.”

Keys said she had to reset completely for the new campaign – and it clearly worked.

She won an Adelaide warm-up event this month and has now amassed 11 straight match wins in Australia – equalling her tally for the whole of 2021.

“Wow, that’s gone well so far,” she said. “I am really proud of myself.”

She will face either Barty or a fellow American, Jessica Pegula, in Thursday’s semi-finals.

World number one Barty, the 2019 French Open and 2021 Wimbledon champion, looks in irresistible form as she chases her first Australian Open crown and the first for an Australian woman in 44 years.

The 25-year-old reached the quarter-finals by comfortably dispatching the 20-year-old giant-killer Amanda Anisimova, who had already accounted for defending champion Naomi Osaka and Tokyo Olympics gold medallist Belinda Bencic.

“I try to adapt my game as best as I can to try and make my opponent uncomfortable,” said Barty. “And that will be no different when Jess and I play.”

Pegula, who revealed last week she had been relaxing with nights at the casino, was a surprise winner over fifth seed Maria Sakkari of Greece.

“That was definitely my best match of the year,” declared the 27-year-old Pegula after reaching the last eight for the second successive year.

Veteran Frenchman Gael Monfils meets big-serving Italian Matteo Berrettini in the last eight and warned the seventh seed: “I’m not quite finished yet”.

The 35-year-old 17th seed Monfils is yet to drop a set in Melbourne while Berrettini sent down 28 aces in sweeping past Spain’s Pablo Carreno Busta.

“He’s feeling good, I’m feeling good,” said Berrettini. “It’s going to be a fight.”