It took just over an hour for Muguruza to dispatch Bertens and the Spaniard will now play either Angelique Kerber or Anastasia Pavlyuchenkova in the quarter-finals.
The 26-year-old Spaniard, who was rusty before the tournament after withdrawing from Hobart with a virus and then lost the first set of her first round clash with Shelby Rogers 6-0, was almost unstoppable on Monday.
Highlights of Muguruza's dominant win against Bertens
Muguruza got off to a fast start, winning the first set in half an hour.
And it only took eight minutes longer - 38 minutes - for the 26-year-old to take the second.
Muguruza created 18 forced errors from Bertens to go a break and a 4-2 lead, before winning the match on the ninth seed's serve at the third attempt.
Muguruza expected a battle
'I'm feeling better every day' - Muguruza's on-court interview after beating Bertens
"Kiki is a tough opponent," she said in her on-court interview.
"We've played many matches and all of them are battles so I was just getting ready to have a tough match and concentrate here.
"Every day I'm feeling a little bit better. The first day I was not feeling well at all but with all my team working to take care of my body each days my health is improving."