Many of the competitors had to play two matches Saturday after rain washed out all but two of Friday's third-round matches.
The seventh-seeded Wozniacki of Denmark bested American Christina McHale 7-6 (7-5), 6-3 in a third-round match earlier in the day, then came back to dismiss Varvara Lepchenko, 4-6, 6-3, 6-4 in the third round.
Fifth-seeded Czech Kvitova dispatched Austrian Tamira Paszek 6-3, 6-2 to reach the semis, while 16th-seeded Safarova of the Czech Republic doused Italy's Roberta Vinci 6-2, 6-2 in another quarterfinal match.
China's 10th-seeded Li bested eight-seeded Italian Sara Errani in a third-round match 6-4, 6-2, then turned around and posted a 6-2, 6-1 rout of Agnieszka Radwanska in the quarters.
Poland's Radwanska had defeated South Africa's Chanelle Scheepers 6-2, 6-4 earlier Saturday.
Swim Week Miami Beach 2014 [PHOTOS]