Aussie Hijikata out-gunned by Isner in Mexico

The Sydneysider was broken in the third and seventh games of the opening set and again at the start of the second, but fought back to push his big-serving opponent to a tiebreaker. 

The 38-year-old Isner, who fired down 19 aces against Hijikata, will face Greece's world No.5 Stefanos Tsitsipas in the next round. 

Fellow Australians Alex de Minaur, the fifth seed, and James Duckworth play their first matches in Los Cobos on Tuesday.

De Minaur will take on Tunisia's Skander Mansouri, while Duckworth faces Otto Virtanen of Finland.