Elena Baltacha appeared in excellent form as she dispatched Melanie Oudin 6-0 6-1 inside an hour to begin the Mercury Insurance Open in Carlsbad, California.
Baltacha dominated as she converted six of her 10 break points in the match.
Ninth seed Roberta Vinci had to come from behind to seal her progression as she beat Bojana Jovanovski 3-6 6-4 6-1.
The only other seed in action was number 16 Polona Hercog due to a rash of withdrawals, including Wimbledon champion Petra Kvitova, Kim Clijsters and Svetlana Kuznetsova.
Hercog was also a winner, beating qualifier Natalie Grandin but only after a lengthy battle, winning 7-6 (7-1) 2-6 6-4.
Vinci advances to face Zheng Jie, who came from behind to beat Mirjana Lucic 5-7 6-2 7-6 (7-3), while Hercog will face Vera Dushevina, a 4-6 6-3 6-4 winner over Aravane rezai.
Wildcard Alexa Glatch had an easier time of beating Ekaterina Makarova 6-1 6-2 while Sofia Arvidsson also won in straight sets, topping Ashley Weinhold 6-3 6-1.
Jill Craybas advanced with a 6-1 6-1 win over Marie-Eve Pelletier, while Coco Vandeweghe needed almost two and a half hours to see off Sorana Cirstea 7-5 6-7 (3-7) 6-3.
Vania King beat Rika Fujiwara 6-1 4-6 7-5 and Virginie Razzano eventually saw off Lucie Hradecka 7-6 (9-7) 6-7 (5-7) 6-1.
© Press Association