Petra Kvitova kicked-off the defence of her Madrid Open title with a 6-2 6-3 victory over Marina Erakovic on the blue clay.
The third seed broke five times in all and fired five aces as she overcame the New Zealander in 67 minutes.
She was joined in the second round by ninth seed Serena Williams, who overcame Elena Vesnina of Russia 6-3 6-1.
The 30-year-old American sent down 13 aces and 40 winners in a straight-forward success, earning her a clash with another Russian - Anastasia Pavlyuchenkova - in the second round.
"I was feeling good," she said. "It's my first tournament in Europe this year and I just hope I can keep up the good form.
"I haven't noticed a difference between the blue and the red clay. I think it's the same, it's just you don't get as dirty."
Serena's sister Venus did not progress though, the former world number one losing to 12th-seeded German Angelique Kerber.
The American wild card was never in the contest as Kerber raced to a 6-4 6-1 win in little more than an hour.
The seven-time grand slam champion was broken six times as she won just 57 per cent of points on her first serve and 33 per cent on her second.
Australia's Samantha Stosur, the US Open champion and fifth seed, finished with a flourish as she battled to a 2-6 6-4 6-0 win over Christina McHale.
Stosur, a strong player on the clay, struggled with her serve in the first two sets and was broken twice in each, but found her range in the decider to claim victory in just under two hours.
China's eighth seed Li Na cruised to a straightforward win with a 6-3 6-1 victory over Spanish wild card Silvia Soler-Espinosa.
Na, the French Open champion, broke five times from 10 break points as he punished her opponent's poor serving.
But 15th-seeded Serbian Jelena Jankovic went out, beaten 4-6 7-6 (7/5) 6-4 by Spanish wild card Carla Suarez Navarro.
In other matches on Monday, there were wins for Petra Cetkovska, Lucie Hradecka, Andrea Hlavackova, Lucie Safarova, Sara Errani and Ekaterina Makarova.