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Raducanu recovered from that setback in the final of August's Challenger tournament in the Windy City, charging to a shock Flushing Meadows triumph, but fellow 18-year-old Tauson awaits her big breakthrough at the Majors.
Tauson took down a former French Open runner-up and current Olympic silver medal winner in reaching the Luxembourg final, beating Marketa Vondrousova in three sets, and now must overcome a player who has been champion at Roland Garros in Ostapenko.
She prised the vital break of serve in the ninth game of the decider against Vondrousova, upping the power in her shots, before serving out for a 6-4 2-6 6-4 victory.
Tauson will be going for a second title of the year, having won the Lyon Open in March.
Defending champion Ostapenko raced to a 6-1 5-1 lead over Liudmila Samsonova but then began to misfire and had to scramble from the brink of being taken to a third set.
Ostapenko eventually prevailed 6-1 7-6 (7-4), having trailed 4-1 in the tie-break, and she will attempt to scoop a fifth WTA title on Monday (AEST). Her most recent came at Eastbourne in the week before Wimbledon.
At the WTA tournament in the Slovenian town of Portoroz, Monday's (AEST) final will feature American Alison Riske and Italy's Jasmine Paolini.
Riske denied Slovenian Kaja Juvan a place in a home final, earning a 6-0 6-4 win in their semi-final, while Paolini sprang a shock by beating Kazakhstan's Yulia Putintseva 1-6 6-3 6-4.