Both of their previous matches this season went three sets, but Muguruza defeated the reigning French Open titlist here in one hour and 25 minutes, avenging her loss to Ostapenko at the Dongfeng Motor Wuhan earlier this month. Here everyone is going to play her best tennis, and every match is going to be like a final, as I have said many times before.
The Romanian described usurping Garbine Muguruza to become the best player in the world as the best day of her life and is determined to retain her status next week.
"We have the top eight players in the world, and everyone is playing insane tennis".
Muguruza said the quality of players made it a very hard event to come away from as the victor.
"I knew that every match is going to be tough here, so I didn't expect an easy group", she said.
"I feel prepared and ready as I regard this as one of the most prestigious tournaments". I'm happy that I got it in the past, and now I'm not that nervous or obsessed.
The year has been like a rollercoaster, with four different major winners and not one player able to dominate in the absence of Serena Williams, who took a break to give birth to her first child. "So I'm going to fight for that".
The Wimbledon champion starts her campaign on Sunday against Latvia's French Open victor Jelena Ostapenko, the pair taking to the Singapore Indoor Stadium court after a White Group opener between Czech Karolina Pliskova and American Venus Williams. The competition is so much greater.
Soon after, the only two 2017 Grand Slam winners competing in Singapore - Muguruza and Ostapenko - did battle, with Wimbledon champion Muguruza downing the 20-year-old.
The Czech Republic's Pliskova, another of this year's world number ones, said it was impossible to tell who will finish on top next weekend. "Is just the best feeling that I ever had in my tennis career so far", the 26-year-old Halep said.
"So this tournament is really going to decide who is going to finish the year world number one". I play better when I'm not thinking about the ranking.