Azarenka took the first set comfortably but faced stiffer resistance in the second from the Ukrainian, who battled hard against the 29-year-old Belarusian on a night when her powerful first serve lacked its usual accuracy.

Azarenka committed 12 double faults and was broken four times but did just enough to edge the defensive-minded Bondarenko, who sent a backhand long on match point to put an end to the marathon match.

Elsewhere, Australian Ajla Tomljanović defeated Spaniard Georgina García Pérez 6-4 6-1 to set up a second-round meeting with second-seeded American Madison Keys.

Nineteen-year-old Sofia Kenin defeated Paraguayan Veronica Cepede Royg 6-4 6-4 and American Danielle Collins fired three aces and won 76 percent of her first service points to dispatch compatriot Danielle Lao 7-6(2) 6-3.

Greek Maria Sakkari cruised to a comfortable 6-2 6-2 win over American Christina McHale, who committed eight double faults and was broken five times.

Tuesday’s action will see 23-time Grand Slam champion Serena Williams face off against Briton Johanna Konta in their first-round duel in San Jose.