Twelve-time champion Rafael Nadal breezed into his 14th Roland Garros quarter-final on Sunday as Dominic Thiem survived an epic five-setter and Alexander Zverev stunned the coronavirus-affected tournament by admitting he played despite being sick and was struggling to breathe.

On a dramatic windswept and chilly day in the French capital, teenagers Jannik Sinner and Iga Swiatek created shockwaves by reaching their maiden Grand Slam quarter-finals.

Nadal beat American qualifier Sebastian Korda 6-1, 6-1, 6-2 to stay comfortably on course for a record-equalling 20th Grand Slam crown.

It was Nadal's 97th win at the tournament against just two defeats since his title-winning debut in 2005.

Teenage kicks: Jannik Sinner celebrates his victory against  Alexander Zverev
Teenage kicks: Jannik Sinner celebrates his victory against Alexander Zverev AFP / Anne-Christine POUJOULAT

"It was a good performance and I am happy with that," said Nadal who has now made his 42nd quarter-final at a major.

He will next face Italy's Sinner, 19 and ranked 75, who defeated Zverev 6-3, 6-3, 4-6, 6-3 to become the youngest men's Grand Slam quarter-finalist since Novak Djokovic in Paris in 2006.

In a tournament turned upside down by the coronavirus, which meant a four-month delay and with a crowd capacity of just 1,000 a day, Zverev admitted he had played despite illness.

The German star, runner-up to Thiem at the US Open, raised questions over whether he should even have been allowed to take to the court when he revealed he had been feeling ill since his win over Marco Cecchinato in the previous round.

Shock victory: Poland's Iga Swiatek celebrates defeating Simona Halep
Shock victory: Poland's Iga Swiatek celebrates defeating Simona Halep AFP / MARTIN BUREAU

"I am completely sick after the match with Cecchinato in the night. I can't really breathe, as you can hear by my voice," said Zverev.

"I'm not in the best physical state. I shouldn't have played."

Sunday shocker: Italy's Martina Trevisan  celebrates
Sunday shocker: Italy's Martina Trevisan celebrates AFP / Anne-Christine POUJOULAT

Zverev, 23, was up to date with his tournament-mandated Covid-19 tests, the French Tennis Federation (FFT) said in a statement. His last one was on September 29.

However, the FFT added that the German "did not consult the tournament doctors before his match".

Zverev's previous coronavirus test was negative. The result was received on September 30.

"Today (Sunday) he received a reminder for his next test, to be carried out within five days of the previous results," the FFT added.

Sunday stroll for Rafael Nadal
Sunday stroll for Rafael Nadal AFP / Thomas SAMSON

Sinner is first player to reach the last eight on his Roland Garros debut since Nadal lifted the trophy in 2005.

"Today was very tough knowing that it's going to be a long match but in the end I'm very happy about my performance," said Sinner.

Third seed Thiem, the runner-up to Nadal for the last two years, was given a major scare by France's Hugo Gaston, ranked at 239, who stunned 2015 champion Stan Wawrinka in five sets in the third round.

Thiem made the last eight for a fifth straight year but had to battle for a 6-4, 6-4, 5-7, 3-6, 6-3 win and will now face Argentine 12th seed Diego Schwartzman for a place in the semi-finals.

"He plays drop shots from another planet," 27-year-old Thiem said of Gaston, the last Frenchman in the draw. "I was lucky to make it through."

World number 54 Swiatek, 19, shocked top seed and title favourite Simona Halep 6-1, 6-2.

Swiatek fired 30 winners past 2018 champion Halep who failed to carve out a single break point.

"I am surprised I could do this," admitted Swiatek after ending the 17-match winning streak of Halep, the overwhelming favourite in the absence of 2019 champion Ashleigh Barty and US Open winner Naomi Osaka and following the injury-enforced withdrawal of Serena Williams.

It was a stunning turnaround for the Pole who won just one game against the Romanian at the same stage in Paris last year, swept off court in just 45 minutes.

Halep, who had arrived in Paris with claycourt titles from Prague and Rome, admitted: "She played really well, it was her match today."

Qualifiers Martina Trevisan of Italy, ranked at 159, and 131st-ranked Nadia Podoroska of Argentina, made the quarter-finals with wins over fifth seed Kiki Bertens and Barbora Krejcikova respectively.

Trevisan, 26, put out Bertens 6-4, 6-4 and will now face Swiatek.

Podoroska, also making her main draw debut, defeated Krejcikova 2-6, 6-2, 6-3 and will next face third seed Elina Svitolina of Ukraine.

The 23-year-old Podoroska, who was ranked at 255 at the start of the season, has now won 42 matches across all tours in 2020 despite the truncated season.

Svitolina reached the quarter-finals for the third time with a 6-1, 6-3 win over France's Caroline Garcia.

Sunday's shocks mean that only four seeds remain in the women's draw -- Svitolina, fourth-seeded Australian Open champion Sofia Kenin, two-time Wimbledon winner Petra Kvitova, seeded at seven, and Tunisia's Ons Jabeur, the 30th seed.