Rain caused the postponement of all main-draw matches scheduled for Monday and just four matches were completed Tuesday. One match -- Vera Dushevina versus Anastasia Pavlyuchenkova -- was in the third set when rainstorms hit again.
Mattek-Sands eliminated sixth-seeded Donna Vekic 6-3, 4-6, 6-2, losing her serve just once in the match. She also claimed three breaks, with two in the final set. Mattek-Sands lost just seven points on serve in the third set.
No. 5-seeded Misaki Doi topped Alberta Brianti 6-2, 6-3 in slightly more than an hour. Doi had six breaks and won 53 percent of the points when Brianti served.
Also in the first round Tuesday, Patricia Mayr-Achleitner defeated Claire Feuerstein 6-3, 6-4 and Karolina Pliskova was a 6-3, 6-2 winner over Casey Dellacqua.
Rosie O'Donnell unveils nearly 50-pound weight loss
The Giudices celebrate Easter as they prepare for jail