Seeded women's players Li Na and Agnieszka Radwanska overcame stubborn resistance to win their first-round matches at the Madrid Masters on Monday.
The second-seeded Na held off Belgium's Kirsten Flipkens 6-1, 7-6 (7) before the third-seeded Radwanska ousted Canada's Eugenie Bouchard 7-6 (3), 6-2 on the clay at the Magic Box.
Na will next face fellow Chinese player Jie Zheng.
In men's first-round play, ninth-seeded John Isner beat qualifier Teymuraz Gabashvili 7-6 (8), 6-4, with the American securing the only break in a match heavy on baseline groundstrokes.
Also, 10th-seeded Kei Nishikori followed up his Barcelona Open triumph with a 6-4, 6-4 win against Ivan Dodig of Croatia.
Jo-Wilfried Tsonga beat fellow Frenchman Edouard Roger-Vasselin 6-3, 4-6, 6-3.