Serena beat American Alexa Glatch 6-2, 6-3 and Venus defeated Israeli Shahar Peer 6-3, 6-3.
Serena won her second straight -- and fifth overall -- Miami title last year by beating Jelena Jankovic in the final. She also won in Miami from 2002-04.
Serena next plays Peng Shuai of China, who beat Italian Mara Santangelo 7-5, 6-3 Saturday. Venus' next match will be against Germany's Anna-Lena Groenefeld, who beat Italian Sara Errani, 6-4, 6-3.
Venus won this event in 1998, 1999 and 2001, beating Serena in the 1999 finale.
Also Saturday, Russian Vera Zvonareva defeated Italy's Tathiana Garbin 6-4, 6-1.
Copyright 2009 by United Press International.