The Latvian won the tournament in 2019 and the result sees her progress into her second final of the year after winning the Eastbourne title in June.
"At some point I stopped playing my game," Ostapenko said in the on-court interview afterwards. "I missed so many balls and I started to rush. [But the key was] to fight to stay in the match.
"I played really well in the beginning but I couldn't close it -- I had to fight and enjoy it."
Information from Associated Press was included in this report.