Osaka will next face last year's beaten finalist Madison Keys, after the highest seed left in the tournament at 14 powered past Spain's Carla Suarez Navarro 6-4 6-3.
From the moment she took the court in her first-round clash last week, Keys played with the determination of someone who was dead set on avenging last year's lopsided final loss to fellow American Sloane Stephens.
She will face No. 20 Naomi Osaka in Thursday's semifinals.
Schiavone, 38, said she accomplished both her goals as a player, which were to win at Roland Garros and reach the top 10 in the world.
Keys will play Japan's Naomi Osaka in the semifinals, a player she has a flawless 3-0 record against, after the 20-year old made light work of Lesia Tsurenko.
Twenty athletes will compete in men's and women's singles and doubles as well as the quad competition, which involves players who have lost some function in at least one of their arms.
Novak Djokovic sweated it out from behind the baseline to beat Australian John Millman 6-3 6-4 6-4 and set up a semifinal with Japan's Kei Nishikori.
Now she has another chance to beat Williams after reaching her first Grand Slam final in NY - a city which has personal significance for the world number 20. The Osaka, Japan, native flew threw the quarterfinal round in less than an hour, beating Ukranie's Lesia Tsurenko 6-1, 6-1. Cilic started well, taking the opening set and going up a break in the second.
"For sure, we will have more athletes like her who are half-Japanese as athletes become more worldwide", said Hiroshi Nakamura, a 65-year-old fan of Osaka, who works at a real estate asset management firm and plays tennis regularly. She also showed impressive tactical awareness against Sabalenka to take some of the pace off her shots against Sabalenka and invite the Belarusian to make more errors, in which Sabalenka duly obliged.
"Today was not my day, obviously", Tsurenko said.
"Being in front of a very energetic crowd tonight was fun", Keys said diplomatically, "and having them behind me was great".
Osaka's leap forward this year has come under the guidance of Sascha Bajin, who previously worked as a hitting partner for Serena Williams and Caroline Wozniacki. "I just tried to think that I've never been in this situation before, [and] I'm just really happy to be here".
Tsurenko, who had 31 unforced errors, went up 40-15 in the first game of the second set, but was broken again.
Nishikori missed last year's U.S. Open with torn tendons in his right wrist.
Speaking after the match, Keys said: "I felt like if I could break, maybe I could get back into it".