Venus Williams held off a fightback from Heather Watson to win through to the quarter-finals of the Mubadala Silicon Valley Classic.
The number three seed is the highest ranked player left in the competition after both Garbine Muguruza and Madison Keys were forced to withdraw due to injury before their second-round matches.
Williams, 38, had raced into an early lead against Watson in San Jose, but the British player rallied in the second set to level the match.
Watson lost her momentum in the decider, however, and the American closed out the match in rapid fashion, winning 6-4 4-6 6-0.
She will next face Greece’s Maria Sakkari, who routed number eight seed Timea Babos 6-0 6-1.
Earlier, number five seed Mihaela Buzarnescu had defeated Amanda Anisimova 7-5 2-6 6-1, while Australia’s Ajla Tomljanovic beat Magdalena Frech 6-4 3-6 6-3.
At the Citi Open in Washington, Magda Linette stunned number three seed Naomi Osaka 6-2 3-6 6-3 to head into the final eight.
The Polish player had been a break down in the final set, but won four consecutive games – and the last 13 points in a row – to close out the upset in two hours and five minutes.
Linette, the world number 62, will take on number seven seed Donna Vekic in the quarter-finals after the Croatian prevailed in an epic deciding tie-break to win 6-2 3-6 7-6 (15/13) against Fanny Stollar.
Meanwhile, Svetlana Kuznetsova beat Ana Bogdan 6-2 6-1, eighth seed Yulia Putintseva defeated Jennifer Brady 7-5 6-2 and Saisai Zheng overcame Ysaline Bonaventure 6-4 6-4.
Former world number one Andy Murray continued his comeback from hip surgery by beating fellow Briton Kyle Edmund in the second round of the Washington Open.
Three-time Grand Slam victor Murray earned a way past reigning British number one Edmund 7-6 (7-4) 1-6 6-4.
He will next play Romania’s Marius Copil in the third round.
Watch highlights of the match below.
Frenchman Benoit Paire was booed off court at the Citi Open in Washington after a spectacular meltdown during his first-round loss to Marcos Baghdatis.
Paire, who is known for his short fuse, lost his temper after missing a smash to drop serve and trail 5-2 in the deciding set.
He sat on the court and smashed one racket before flinging it across the tarmac, and then walked to his chair, kicking that before smashing another racket and sending it flying.
Baghdatis, himself no stranger to a racket smash, walked over to Paire apparently to try to calm him down but, after making no effort to return a serve on match point in the next game, the Frenchman smashed a final racket before shaking hands.
When the crowd were encouraged at the end of the match to show their appreciation for Paire, a 29-year-old ranked 55, they responded with loud booing.