Saville, who continues to charge back towards the top 100 after experiencing a series of injury setbacks, upset 58th-ranked Zhu Lin on Monday for the second time in 2024, 6-3 6-3. The 29-year-old also defeated the Chinese baseliner in January on her way to the semi-finals in Hobart.
"I definitely had to run a lot today," said Saville, who converted all four of her break-point opportunities against Zhu.
"But that's basically my game. I'm glad that I took opportunities when I could, took my own chances and made it happen."
🔛�— wta (@WTA) @Daria_gav secures her spot into the next round after defeating Zhu in straight sets 6-3, 6-3.#SanDiegoOpen pic.twitter.com/oYjC6ciWq0February 27, 2024
It was the third win in as many days for Saville, who came through the qualifying rounds.
"I always think that qualifiers are pretty dangerous," the current world No.148 said.
"I've had some of my best runs from playing qualifying."
Boulter earned her first win over Ukraine's Lesia Tsurenko in four career match-ups, 6-3 6-1 in 71 minutes.
"I knew today was going to be an absolute battle," said Boulter, who collected her 10th victory over a top-50 opponent.
"I just came out and tried to compete and do the best I could. I don't think either of us played our best tennis, but sometimes it's about finding a way, and I did that."
The 36th-ranked Tsurenko was indeed playing some of her best tennis earlier this month in Doha, where she stunned sixth-ranked Ons Jabeur in the second round. However, the 34-year-old was unable to take the court for her round-of-16 matchup with Naomi Osaka due to a right elbow injury.
Elsewhere, there were round-of-32 victories for German qualifier Jule Niemeier, Canada's Marina Stakusic and Xinyu Wang of China.
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