Pironkova extended the recent frustrations of 11th-seeded Roberta Vinci with a 6-3, 6-3 win in which she has six breaks in nine Vinci serving games. Pironkova won 55 percent of the points off Vinci's serve, nearly as high a percentage as when Pironkova served. Vinci is 0-4 this year.
Cetkovska knocked off No. 14-seeded Sloane Stephens 7-5, 6-1, taking more than 70 percent of the points in the second set. Cetkovska dropped serve twice in the first set but had three breaks to claim the lead. She finished 5-of-7 in break opportunities.
Venus Williams rolled to a 6-2, 6-2 decision over Petra Martic in 63 minutes. Williams won three-quarters of the points on serve and faced only one break point.
Li Na, assured next week of moving to No. 2 in the world rankings, is the No. 1 seed this week over a field that includes seven Top 10-ranked players.
No. 1-ranked Serena Williams and second-ranked Victoria Azarenka, who played for the tournament title last year (with Azarenka winning), are out due to injuries and No. 5 Maria Sharapova is working on a broadcast team at the Sochi Olympics.