However, her older sister Venus was forced to withdraw ahead of her match against Spain's Anabel Medina Garrigues due to a back injury.
Chinese fifth seed Li Na crashed out, losing 6-3 6-2 to 18-year-old American Madison Keys.
Former world No. 1 Caroline Wozniacki continued her decline, as the Danish 10th seed lost 6-2 6-4 to another Kazakh player, Yaroslava Shvedova.
Czech eighth seed Petra Kvitova, the 2011 Madrid champion, went through to round two along with Poland's world No. 4 Agnieszka Radwanska.
Meanwhile, veteran Tommy Haas won the Munich Open on Sunday, beating fellow German Philipp Kohlschreiber 6-3 7-6 (7-3) 13 years after losing in his previous final appearance in the clay event.
The 35-year-old, a former world No. 2, will now climb to 13th in the rankings.
It was the first all-German final in Munich since 1965, and Kohlschreiber was unable to defend his title -- having also won it in 2007.
In Oeiras, Stanislas Wawrinka upset top seed and world No. 4 David Ferrer 6-1 6-4 to win the Portugal Open on Sunday.
It was the 28-year-old Swiss' fourth career title, and first since January 2011.