Defending champion Venus Williams was forced to battle for the second successive match to book her place in the final of the Abierto Mexicano Telcel tournament.
The top-seeded American recovered from a mid-match slump to overcome world number 164 Edina Gallovits 6-4 2-6 6-2 on the red clay in Acapulco.
Williams, who will meet eighth seed Polona Hercog in the final, had also struggled in her quarter final when she recovered from 5-1 down in the third set to defeat the 399th-ranked Spanish qualifier Laura Pios Tio.
Hercog, 19, reached her first ever WTA Tour final when she defeated fifth seed Carla Suarez Navarro 6-3 7-5.