Wimbledon champion Venus Williams breezed through her first match since winning at the All England Club, beating Sania Mirza in California.
Williams came through 6-3 6-2 to reach the quarter-finals of the Bank of the West Classic in Stanford.
She goes on to face Serbian seventh seed Jelena Jankovic, who beat American Amy Frazier 6-0 6-3.
Patty Schnyder had a 6-4 7-5 win over Marion Bartoli, who was treated for left-knee tendonitis between sets.
In Wednesday's other match, French sixth seed Nathalie Dechy defeated American Lisa Raymond 3-6 6-3 6-4.
Williams felt there was still room for improvement despite her comfortable win over Mirza.
"My serve definitely picked up," she said. "I played a lot better than I expected, but I also didn't feel I played that well."
Top seed Lindsay Davenport plays her first match against Anna-Lena Groenefeld of Germany on Thursday.