Li Na and Agnieszka Radwanska, the second and third seeds in the women's singles, were victorious in the first round of the Madrid Open on Monday.
Li, the world number two, beat Kirsten Flipkens 6-1 7-6, while Radwanska was a 7-6 6-2 winner over Eugenie Bouchard.
Ninth seed Dominika Cibulkova is out after losing 6-4 6-0 to Sam Stosur.
The night session was preceded by a minute's silence in memory of former British number one Elena Baltacha, who died on Sunday of liver cancer aged 30.
Earlier, ninth seed John Isner beat qualifier Teymuraz Gabashvili 7-6 6-4 in the men's draw, while Kei Nishikori followed up his Barcelona Open triumph with a 6-4 6-4 win over Ivan Dodig.
Jo-Wilfried Tsonga, seeded 11th, beat Edouard Roger-Vasselin 6-3 4-6 6-3 in an all-French clash.