Fabio Fognini's Los Cabos Open title defence came to an end with a loss to the in-form Taylor Fritz, while Guido Pella and Diego Schwartzman set up a semifinal showdown.
Fognini, last year's champion in Mexico, bowed out in the quarterfinals with a 6-1 7-6 (7-1) defeat to Fritz on Thursday.
Fritz is coming off a run to the Atlanta Open final and got the better of Fognini to record his 12th victory in his last 14 matches.
The 21-year-old American saved five break points against Italian top seed Fognini, who had won their only previous meeting last year.
Fritz will face Radu Albot in the semifinals after the Moldovan seventh seed beat 2017 runner-up Thanasi Kokkinakis 6-3 6-3.
Pella, the second seed, edged past qualifier Kwon Soon-woo 4-6 6-1 6-2, breaking serve six times.
He will meet Schwartzman in an all-Argentinian last-four clash after the third seed crushed Mikhail Kukushkin 6-1 6-2.
Pella and Schwartzman were the second seeds in the doubles at the tournament, but lost in the quarterfinals on Thursday.
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