Nao Hibino was a shock first-round casualty at the Monterrey Open, while fellow seed Ann Li advanced.

Seeded ninth for the WTA International tournament, Japan's Hibino was upstaged 3-6 6-2 6-3 by Jasmine Paolini on Monday.

American eighth seed Li, however, had no such trouble in her 6-3 7-5 victory over Arantxa Rus on the outdoor hard courts.

Coco Vandeweghe – the 2017 Australian Open semi-finalist – suffered another early exit in Mexico.

After being ousted by Mihaela Buzarnescu in the opening round in Guadalajara last week, former world number nine Vandeweghe was eliminated 6-3 6-2 by Canadian teenager Leylah Fernandez.

Fernandez will face either top seed Sloane Stephens or lucky loser Kristina Kucova in the second round.

Anna Karolina Schmiedlova, Nina Stojanovic, Viktoria Kuzmova, Lauren Davis and Tamara Zidansek also progressed from the opening round.