The 24-year-old Baptiste claimed her first victory over a top-five player, beating Sabalenka 2-6 6-2 7-6 (8-6) to hand the defending champion only her second defeat of the season.
Baptiste, the 30th seed, will now face world No.9 Mirra Andreeva, after the Russian got past Canada's Leylah Fernandez 7-6 (7-1) 6-3 in the quarter-finals earlier on Tuesday (local time).
"Incredible. Super proud of myself," Baptiste said.
"It was a super tight match, 7-6 in the third.
"I had to fight off match points. I'm really happy right now.
"It just shows me where my game lies. I've always believed it. Now I'm starting to put it into action and the world is seeing it as well."
"It was a tough match. She played great," Sabalenka said.
"I played great. I think I had some opportunities in the third set. I felt like I was maybe a little bit rushing the point over there. But it's OK, sometimes I guess you have to learn, take the bad stuff from this week and move on."
The defeat of top-seeded Belarusian Sabalenka is the latest upset at the WTA 1000 clay tournament, which has seen the top seven seeds knocked out.
Baptiste is guaranteed to reach a career-high ranking of at least No.24 after also making the Miami Open quarter-finals last month, where she lost to Sabalenka.
- with AP
