French Open runner-up Chwalinska, who was Swiatek's junior doubles partner, will now face Sonay Kartal in the final after the British surprise packet beat Jelena Ostapenko 7-6 (11-9) 7-6 (7-5) in Saturday's first semi-final at the Chinese WTA 1000 event.
Swiatek was 5-3 ahead in the first set but fellow 25-year-old Chwalinska saved two set points and took a 6-5 lead before the six-time grand slam winner had to take a medical timeout.
After receiving treatment, Swiatek continued the match with a bandaged left thigh, but found it difficult to put pressure on her leg and struggled to chase returns across the court.
She completed the match with encouragement from her team and the two players, who have known each other since they were 10, shared a quiet handshake after their first competitive clash in 10 years.
"She is a great champion, living legend, she won everything. So it was a great honour for me to share the court with her today," an emotional Chwalinska said of Swiatek.
"The fact that I actually won against her is actually crazy for me."
With Swiatek losing, world No.6 Elina Svitolina has secured her place in the WTA Finals, becoming the seventh player to qualify for next month's year-ending championship, with only one spot now still up for grabs.
Earlier, former French Open champion Ostapenko was left ruing her mistakes as she squandered 4-1 leads in both sets to lose to world No.170 Kartal, who is ranked 136 places below the Latvian.
Ostapenko was undone by her 41 unforced errors, including two straight double faults while serving for the first set. She hit the ground with her racket, frustrated with wayward and netted returns, as Kartal stayed calm to reach her second final on the tour.
"At times she's unplayable and sometimes you just have to ride the wave. Mentally, I think this is one of the best performances I've had in my career," said the 24-year-old Kartal, who only returned in September after a six-month absence due to a back injury.
For both Kartal and Chwalinska, it will be a first WTA 1000 final appearance in Sunday's championship match.
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