Nadal had earlier made light work of Sebastian Korda to book his passage to the next round, dropping just four games in three sets as he comfortably dispatched his 20-year-old opponent.
The Spaniard is going for a 13th title in the French capital and, while he was clearly a cut above, Korda's 48 unforced errors certainly aided his cause on Sunday.
But the day belonged to 19-year-old Sinner, who looks destined for big things.
SINNER THROUGH BUT ZVEREV IN THE SPOTLIGHT
Reigning Next Gen ATP Finals champion Sinner was in electrifying form on Court Suzanne-Lenglen, beating Zverev 6-3 6-3 4-6 6-3.
Sinner converted five of his six chances to break Zverev, who appeared curiously underwhelming on the day. He hit just 20 winners, a little over half of Sinner's 39, highlighting the gulf in decisiveness.
In claiming victory, Sinner became the youngest male player to reach a grand slam quarter-final in 14 years and he felt that, having trained with Zverev on occasion in the past, he was well prepared.
"It has been tough. We have practiced sometimes in Monaco, so we know [each other] quite well," said Sinner on court. "Today was very tough, knowing that it was going to be a long match. At the end, I am very happy about my performance."
But Zverev controversially revealed after the match that he had been suffering with a fever and that he should not have even taken to the court.
The German claimed he had tested negative for coronavirus, though he did not specify when his most recent test was.
NADAL AWARE OF HIS EXCELLENCE
As he prepares for his quarter-final with Sinner, Nadal is well aware he is in imperious form.
Korda offered little resistance on the whole as the second seed ran out a 6-1 6-1 6-2 victor against a player who idolised him growing up – so much so he even named his cat 'Rafa'.
And although the American got his claws into Nadal with a couple of early break chances, the favourite was soon purring and took just 40 minutes to take a one-set lead.
Nadal only struck nine winners over the first two sets, but Korda's error count continued to rise and give his opponent a boost.
The 19-time major champion was left feeling pretty good about his form afterwards as well.
"Well, I'm in the quarter-finals without losing a set and having very positive scores. So, I can't complain at all. So, I'm happy for that," he said.
He then went on to consider the threat posed by Sinner, adding: "He's young, he's improving every single week. So, he's playing better and better and better. It will be a big challenge. It will be the first time playing against him on the tour. I practiced with him a couple of times, he has an amazing potential, he moves the hand very quick and he's able to produce amazing shots."
THIEM FIGHTS BACK
Third seed Dominic Thiem had to dig deep to see off Hugo Gaston in five after throwing away a two-set lead against the world number 239.
Eventually Thiem progressed 6-4 6-4 5-7 3-6 6-3, emerging victorious after just over three and a half hours on court.
French wildcard Gaston received a standing ovation from his home support on Court Philippe-Chatrier, with the fans enamoured with the underdog as he pushed one last year's runner-up all the way.
Thiem acknowledged that he was fortunate to come through the test.
"I think I stayed pretty calm even though it was a tough match mentally, physically. I just read before that he played 58 drop shots. I think only three or four of them went into the net, so I made more than 50 full sprints to the net. So that was really, really tough," he said.
Up next for Thiem is a quarter-final with Diego Schwartzman, one of his closest allies on the ATP Tour, with the Argentinian seeing off Lorenzo Sonego with relative ease 6-1 6-3 6-4.
"I'm happy of course to face one of my best friends from the tour in the quarter-finals," Thiem added.
"From my perspective, it's all about recovery. I'm not running on a full tank anymore. That's for sure. So, I try to recover as good as I can. If I'm able to do that, if somehow I don't make it until Tuesday, I think he's going to be the heavy favourite."