MADRID, Spain - Reigning champion Simona Halep edged closer to a third consecutive Madrid Open title by beating Belgium's Elise Mertens in the second round on Tuesday (early on Wednesday morning, South African time).
Halep, the winner here in 2016 and 2017, was made to work harder in the second set on Manolo Santana but the world number one's 6-0, 6-3 victory was never in doubt.
Kristyna Pliskova of the Czech Republic will now await Halep in the last 16 as the Romanian continues to prepare for the French Open, where she has twice gone the distance only to finish runner-up.
Halep won the first eight games in a row to lead 6-0, 2-0, with her clay-court counter-attacking too strong for the 22-year-old Mertens to handle.
Mertens offered some late resistance as her opponent's concentration wavered, but a double fault confirmed Halep's victory in a brief one hour and 11 minutes.
"I think I played well again," Halep said. "It is the second match of the tournament. I have a great feeling."
Earlier, Petra Kvitova battled to a 6-3, 7-6 (10/8) victory over Puerto Rico's Monica Puig to register her seventh consecutive win.
Kvitova's hard-hitting game lends itself more to the faster surfaces but after lifting the title on clay in Prague at the weekend, she has maintained her momentum here and will meet Estonia's Anett Kontaveit in round three.
Home favourite Garbine Muguruza staged a comeback from a set and a break down to beat Donna Vekic 2-6, 6-4, 6-1 and reach the third round for the first time in her career.
The two-time Grand Slam champion was in trouble when she dropped serve in the fifth game of the second set, but won 10 of the next 12 games to race to victory.
Dangerous Russian Daria Kasatkina awaits the world number three in the last 16 after a comfortable win over Sorana Cirstea.
Fourth seed and reigning Italian Open champion Elina Svitolina slumped to a surprise 6-2, 6-7 (3/7), 6-4 loss to Spaniard Carla Suarez Navarro in the second round.
The Ukrainian world number four will now prepare for the defence of her title in Rome next week, while Suarez Navarro will face Bernarda Pera, after the American brushed aside Johanna Konta 6-4, 6-3.
Del Potro makes winning return
Juan Martin del Potro made a winning start to his clay-court season by seeing off Damir Dzumhur in his first match since losing in the Miami Open semi-finals to John Isner in March.
The former US Open champion, who has won two titles this year including at Indian Wells, had far too much for his Bosnian opponent in a comfortable 6-3, 6-3 win.
Del Potro admitted that his persistent wrist injuries make clay more difficult for him than other surfaces.
"On clay you can't use the slice much, which is a blow because I've been using it more for my wrist problems," he said.
"For now my wrist is responding well, I'm still having treatment every day. I'm calm, because I've been doing well."
The Argentinian, twice a semi-finalist in Madrid, will take on Dusan Lajovic in the last 16 after the Serbian edged out Richard Gasquet 7-6 (7/1), 7-6 (7/1).
World number four Grigor Dimitrov was beaten in a tight second-round encounter by former Wimbledon runner-up Milos Raonic, who is playing his first tournament since withdrawing from the Monte Carlo Masters with injury.
The big-serving Canadian grabbed the first break of the match in the 11th game, and despite seeing Dimitrov fight back to force a decider, he closed out a 7-5, 3-6, 6-3 win.
Elsewhere, South Korean rising star Chung Hyeon suffered a shock 6-0, 6-2 first-round thrashing at the hands of Dutchman Robin Haase.
Chung's fellow Australian Open semi-finalist Kyle Edmund beat Daniil Medvedev 6-4, 6-0 to set up a clash with former world number one Novak Djokovic, who beat Kei Nishikori on Monday.