Wednesday's day session in San Diego saw a trio of Americans -- Danielle Collins, Sofia Kenin and Emma Navarro -- book their spots in the quarterfinals.
Collins was a 2-6, 6-3, 6-4 winner over Jelena Ostapenko in a match between a Grand Slam finalist and champion, while Kenin also won in three sets, 1-6, 6-4, 6-2, over Katie Volynets in a match between two wild cards.
Both Collins and Kenin trailed by a set and a break in their eventual wins. Collins was 2-0 and 3-2 down in the second set, and later, 3-1 down in the third, while Kenin was a break down at 2-1 in both the second and third sets of her first career match against Volynets.
The resurgent 2020 WTA Player of the Year Kenin is through to her second quarterfinal of 2023, where she'll face Anastasia Potapova, who upset No.1 seed Ons Jabeur in other second-round action.
Navarro, the youngest of the three at age 22, reached her first career WTA 500 quarterfinal with a 7-5, 6-4 win over Aliaksandra Sasnovich in a match between qualifiers.
It was a measure of revenge for world No. 61 Navarro, who lost to Sasnovich 3-6, 6-4, 7-5 in Cleveland the week prior to the US Open despite leading 5-0 in the third set. She was 4-2 down in the opener and won the match in straight sets despite nearly letting a 5-2 lead go in the second set.
Navarro failed to serve out the win at 5-3, and denied Sasnovich three points for 5-5 before wrapping up the win on her first match point.