Madrid - Reigning champion edged closer to a third consecutive Madrid Open title by beating Belgium's Elise Mertens on Tuesday.
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.
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 the lifting the title on clay in Prague at the weekend, she has maintained her momentum here.
A tight second set was decided by a tie-break and Kvitova almost threw it away when she served two double faults. The first came on her own match point and the second after a malfunction with the court's sound system meant music played just as she was about to serve.
But the world number 10 recovered her composure to seal a place in the next round, where she will meet either Estonia's Anett Kontaveit or Aliaksandra Sasnovich of Belarus.