The 20-year-old was nowhere near her level from earlier in the week but Sakkari was also determined and showed the kind of performance that saw her end Naomi Osaka's 23-match winning streak in March in Miami.
"No, I'm speechless. It's a dream come true. It's a really nice feeling and I couldn't have done it without my team and their support. I just want to thank them, we still have a long way to go, but we've taken a step forward today," said Sakkari, who was overcome with emotions as she sat down on her bench after the win, her face buried in her towel.
Krejcikova overcomes Gauff
Sakkari will next take on Barbora Krejcikova, who survived a wild first set before she blasted into a maiden Grand Slam semi-final with a 7-6(6), 6-3 victory over 24th-seeded Coco Gauff.
The former doubles world No.1 extended her current winning streak to 10 consecutive matches, having picked up the title in Strasbourg on the eve of the tournament.