Sinner, 19, dispatched his Monte Carlo practice partner 6-3, 6-3, 4-6, 6-3 in just over three hours to advance.
"It was tough playing against him as we know each other but I am pleased with my performance," he said.
Sinner, the world number 75, beat the 11th seed David Goffin in the opening round in Paris in straight sets before disposing of Benjamin Bonzi and Frederico Coria in the same way in the second and third rounds respectively.
Calm
After losing his first set of the tournament on Sunday on Court Suzanne Lenglen, he showed remarkable sang froid to continue his strategy of blistering ground strokes that forced an equally powerful Zverev onto the back foot.
"It's the best of five sets," said Sinner. "If you lose one set you just try and keep going. Even in the third set I knew I was still playing well.
"I tried to be focused in the first service game in the fourth set, which I did, and then it went quite well."
Indeed. After holding his opening service game, he claimed Zverev's to go 2-0 up. A game lasting 11 minutes pushed him 3-0 ahead and he kept his nose in front to become the first man since Nadal in 2005 to progress to the last eight in their first appearance at Roland Garros.
The future is bright 🇮🇹@janniksin is the first man to make the final 8 on his debut since Nadal, his next opponent, in 2005. He defeats Zverev 6-3 6-3 4-6 6-3.#RolandGarros pic.twitter.com/FWqif1NIt8
— Roland-Garros (@rolandgarros) October 4, 2020
Nadal reached the quarters for the 14th time with a 6-1, 6-1, 6-3 defeat of 20-year-old Sebastian Korda.
"I'm very happy with a good match against a good player," said Nadal before predicting a bright future on the senior circuit for the American, who despite being the son of former world number one Petr Korda, admitted it was Nadal who inspired him to become a player.
"It's an honour for me," said Nadal. "All of our generation of players try to be passionate and to try our best to inspire the young generation."
