Alexandrova, who had a 4-1 lead when Sakkari bowed out, will face Anett Kontaveit in Sunday's final.
Tournament organizers said Sakkari cited dizziness for the stoppage. She is ranked seventh in the world and secured a place at the season-ending WTA Finals earlier this week.
Alexandrova reached her first tour-level final since winning the Shenzhen Open in January 2020 and has a 1-1 career record in finals.
Kontaveit will bid to win a third title in as many months after beating Marketa Vondrousova 6-3, 6-4 in the other semifinal. The Estonian took a big lead early in both sets but took her time closing out the match on the fourth match point.
"I thought it was a very difficult match. I was trying my hardest, and Marketa is such a nice girl and a tough opponent and a tricky opponent to play against," Kontaveit said. "I'm so happy to be in the final.''