Unseeded Sakkari was speechless after defeating top seed Swiatek 2-6 6-4 7-5.
Sakkari reached a career-high world ranking of No. 3 four years ago before falling to No. 52 and has not won a match since March 2024.
But after a nervous start, Sakkari recovered and reached the semifinals.
“I have nothing to say because it’s been a while since I’ve had a big win like I did today,” she said.
“When you drop down the rankings and your tennis isn’t good, you start to doubt yourself.
“You think you’re never going to beat those guys again.”
The Greek player will face Czech Karolina Muchova in the other semi-final. The 14th seed swept Russian Anna Kalinskaya 6-3 6-4.
Latvian Ostapenko defeated another unseeded player, Italian Elisabetta Cocciaretto, 7-5 6-4 in the quarterfinals.
