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.
In other matches on Monday, Lucia Hradecka of Czech Republic beat China's Peng Shuai 6-4 5-7 6-4 while compatriot Andrea Hlavackova saw off Anastasia Rodionova 6-1 6-4.
Russia's Ekaterina Makarova also went through after beating Galina Voskoboeva 6-2 7-6.
