Mexican fifth seed Renata Zarazua, who sent Madison Keys home in first round of the US Open last month, knocked off top-seeded Brazilian hopeful Beatriz Haddad Maia, 7-6(5), 6-3 in a two-hour, 15-minute match.
Zarazua rallied from a 5-3 deficit in the first set and a 5-4 disadvantage in the tiebreaker to capture the first set, then broke Haddad Maia in the penultimate game of the match to prevail.
Unseeded Indonesian upstart Janice Tjen surprised the Philippines' No. 3 seed Alexandra Eala, 6-4, 6-1; No. 6 Francesca Jones of Great Britain took out No. 2 Solana Sierra of Argentina, 6-3, 6-4; and unseeded Frenchwoman Tiantsoa Rakotomanga Rajaonah eliminated Hungary's No. 8 seed Panna Udvardy, 6-2, 6-4.
Tjen saved both break points she faced and was a perfect 12-for-12 against Eala on second returns. She will face Jones in the Saturday's semi-finals, while Zarazua takes on Rakotomanga Rajaonah.
Guadalajara Open
Four unseeded players will contest the semi-finals in Guadalajara, Mexico, after the event's upset trend continued.
The Czech Republic's Nikola Bartunkova downed fourth-seeded Magdalena Frech of Poland 7-5, 6-4 in the last match of the night after France's Elsa Jacquemot ousted sixth-seeded Tatjana Maria of Germany 3-6, 6-4, 6-4.
The United States' Iva Jovic saved a match point in the third-set tiebreaker and edged Andorra's Victoria Jimenez Kasintseva 6-3, 3-6, 7-6(6). Colombia's Emiliana Arango got past Canada's Marina Stakusic 6-2, 6-3.
Earlier in the day, Stakusic upset No. 3 Latvian Jelena Ostapenko, 6-4, 6-7(6), 6-2 in the completion of a second-round match that was suspended Thursday night.
On Saturday, Jacquemot will oppose Arango before Bartunkova faces off with Jovic.