Sara ErraniTop seed Sara Errani was dumped out of the Abierto Monterrey Afirme in the second round by Estonian Anett Kontaveit.
Italian Errani, who survived a big scare in the first round, was comprehensively beaten 6-1 6-3 in under an hour by the world number 91.
Errani, ranked 17 in the world, had her serve broken three times in each set by Kontaveit, who had failed to progress past the first round in her last two tournaments.
Kontaveit's quarter-final opponent will be qualifier Nicole Gibbs, who was leading fellow American Christina McHale 7-6 (7/5) 6-7 (4/7) 3-0 when the latter retired.
Second seed Caroline Wozniacki made no mistake in her second round match as she battled to a 6-4 6-4 victory against Croatia's Mirjana Lucic-Baroni.
The Dane took four of the five break points she earned to set up a last-eight meeting with Britain's Heather Watson.
France's Caroline Garcia, the fifth seed, will meet compatriot Pauline Parmentier in the quarter-finals after beating Israeli qualifier Julia Glushko 6-1 6-2.
Parmentier followed up her first-round victory against third seed Anastasia Pavlyuchenkova by seeing off Monica Puig 6-3 6-4.

Source: WTA Tennis