Top seed Mirjana Lucic-Baroni succumbed to a stomach virus as she retired against Lesia Tsurenko in the semi-finals at the WTA Abierto Mexicano Telcel.
Croatian veteran Lucic-Baroni, 34, retired when trailing seventh seed and Ukrainian Tsurenko 5-0 in the opening set in Acapulco on Friday.
Competing in her second successive semi, having reached the final four at the Australian Open in January, Lucic-Baroni was looking to advance to her first WTA Tour decider since losing to Caroline Garcia in Strasbourg in May last year.
But Lucic-Baroni was unable to continue against Tsurenko, who will now face second seed Kristina Mladenovic in Sunday's showpiece.
Mladenovic withstood a tough challenge from Christina McHale to book her spot in the final following a tense three-set battle.
France's Mladenovic outlasted fifth seed McHale 7-5 4-6 6-2 as she looks to build on her maiden WTA title, having triumphed at the St. Petersburg Ladies Trophy in February.
Mladenovic converted five of 16 break points against the American after two hours, 22 minutes on court.