World number one Simona Halep beat Belgium's Elise Mertens on Tuesday to reach the third round of the Madrid Open. The Romanian won 6-0 6-3 in 71 minutes to end Mertens' 13-match winning streak.
Halep won the first eight games of the match and hit 23 winners as she set up a meeting with Czech Kristyna Pliskova.
Earlier, world number 10 Petra Kvitova won her seventh consecutive match with a 6-3 7-6 (10-8) victory over Puerto Rico's Monica Puig.
Czech Kvitova, who won the Prague Open on Saturday, had lost both her previous meetings with Puig. Merten's winning streak included titles in Rabat, Morocco and Lugano, Switzerland.
However, Kvitova struck 30 winners and, despite nine double faults, won 68% of points on her second serve. She will play either Daria Kasatkina or Sorana Cirstea in the next round.