Second seed Marie Bouzkova suffered a shock first-round exit at the Monterrey Open losing in straight sets to world number 100 Anna Karolina Schmiedlova on Monday.
The Slovakian triumphed 6-4 6-2 in one hour and 46 minutes over the Czech who was a runner-up at this event in 2020.
Schmiedlova will take on American qualifier Caroline Dolehide in the second round after she knocked off Jule Niemeier 6-1 6-0.
Dolehide's dominance was impressive given she is ranked 206th in the world compared to 2022 Wimbledon quarter-finalist Niemeier at 69th.
Secures the win in Monterrey!— wta (@WTA) February 28, 2023
Schmiedlova knocks out No.2 seed Bouzkova in straight sets.#AbiertoGNPSeguros pic.twitter.com/NOLtEqCLFK
Fifth seed Zhu Lin got past Hungary's Anna Bondar 6-4 7-6 (7-4), setting up a second-round clash with Canada's Rebecca Marino after she beat local wildcard Fernanda Contreras Gomez 7-6 (7-4) 7-6 (7-4).
Belgium's Ysaline Bonaventure triumphed in two hours and 20 minutes over Greek qualifier Despina Papamichail 7-6 (7-5) 4-6 6-1.
British qualifier Heather Watson toppled Danka Kovinic 7-6 (7-2) 6-4 in the first round of the ATX Open in Austin.
Seventh seed Alycia Parks was eliminated 6-4 4-6 6-4 by Swedish wild card Mirjam Bjorklund.
Wildcard Mirjam Bjorklund is moving on to round 2! #ATXopen pic.twitter.com/dnoiG4Qk0Y— ATX Open (@AtxOpen) February 27, 2023