See main article: 2018 Silicon Valley Classic.
Madison Keys was the defending champion, but withdrew due to a wrist injury.
Mihaela Buzărnescu won her first WTA Tour singles title, defeating Maria Sakkari in the final, 6–1, 6–0.
The top four seeds received a bye into the second round.
Note: Aryna Sabalenka, who would have been placed in the entry list on the initial entry cutoff date of June 18, 2018 and seeded 7th, entered late and played the qualifying tournament. But she was eliminated in qualifying matches.