London Olympic hopefuls had mixed results at the WTA hardcourt event in Carlsbad, which offers them a final chance to warm up for the Summer Games tennis competition at Wimbledon.
Fifth seed Christina McHale, due to join Venus and Serena Williams and Varvara Lepchenko on the US Olympic team, battled past Australian Jarmila Gajdosova, 7-6 (7/5), 7-5.
New Zealand's Marina Erakovic, also headed to the Olympics, beat British Olympic hope Anne Keothavong 6-4, 6-0 in just over an hour and a quarter with five breaks of the Brit's serve.
"It was a tricky first round. Anne comes out hitting some big balls," said the Kiwi ranked 47th.
"She doesn't give you much rhythm, but just getting into the match and settling down helped."
McHale may have picked up some extra fighting spirit from her visit on Monday to the retired aircraft carrier USS Midway, now a floating museum docked in nearby San Diego harbor.
McHale, the world number 27 who reached the Wimbledon third round, recovered from a break down against Gajdosova to take the opening set with a backhand winner down the line.
The American took the second thanks to a break of serve in the penultimate game, winning after almost two hours with nine aces.
"It wasn't easy out there, my opponent played really well," McHale said. "It was hard to get a read on her serve.
"I'm just happy to have pulled that one out. I just kept fighting. All of the games were really close."
The 20-year-old admitted that the Olympic excitement has yet to strike her.
"It doesn't seem real now, but I guess it will hit me when we're on the plane to London."
Seventh seed Yanina Wickmayer, a semi-finalist last week up the coast at Stanford and also London-bound, had to retire with a back injury after dropping the first set against qualifier Chan Yung-Jan of Taiwan 7-6 (8/6).
Chan next faces Britain's Heather Watson, who beat Eleni Daniilidou of Greece 6-3, 6-3.
American Coco Vandeweghe, runner-up to Serena Williams at Stanford on Sunday, was brought back to earth as she fell to eighth-seeded South African Chanelle Scheepers 6-2, 7-6 (7/4).
Vandeweghe had eight aces but also six double-faults, converting only one of her 10 break chances.
American Vania King, a 6-1, 6-4 winner over Taiwan's Chang Kai-Chen, will be the first opponent for top seed Marion Bartoli of France, who received a first-round bye along with second seed Dominika Cibulkova, third seed Jelena Jankovic and fourth seed Nadia Petrova.