The 2021 US Open winner was featuring in her first semi-final since that fairytale triumph at Flushing Meadows, and took the opening set 6-4 after making a flying start on Saturday.
Ostapenko then fought back to level the match, with Raducanu first appearing to struggle with her movement when she was a break up in the second, forcing her to take an off-court medical timeout.
The 19-year old later retired citing a left glute injury when 3-0 down in the decider, ending her confidence-boosting run in Seoul and teeing up a final meeting between the top two seeds.
Indeed, Alexandrova enjoyed a more routine outing in her meeting with Wimbledon semi-finalist Tatjana Maria, downing the German 6-2 6-4 to advance to her second final of the year.
At the Pan Pacific Open in Tokyo, meanwhile, Chinese teenager Zheng Qinwen reached her first WTA Tour final with a hard-fought win over world No.13 Veronika Kudermetova.
Having required more than three hours to seal her 5-7 6-3 7-6 (7-3) triumph, the world No.36 said: "After the match when I won the last point, the feeling was incredible.
"The opponent, she's playing unbelievable tennis. She has a really good serve and hits the ball hard, she moves well. It's my first time in the final. I'm so happy."
Her compatriot Zhang Shuai was unable to replicate those exploits, however, as Liudmila Samsonova eased into her third WTA final of the year with a 7-6 (7-4) 6-2 win.
In-form Samsonova has won both of her previous final appearances this year – each of which came last month – and is 3-0 in showpiece matches for her career.