At her first appearance in Singapore, the world number two won all three round-robin matches before losing a tight semi-final to an inspired Agnieszka Radwanska, while last year she was eliminated early after losing two of her three ties.
On both occasions, the eventual champion (Radwanska in 2015 and Dominika Cibulkova last year) sneaked into the knockout stage with losing 1-2 records in pool play.
"Well, I think it's very important to start with a win," the Wimbledon champion told reporters.
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"What I learned from the past is that every game counts, every set, because at the end only two (players per group) are going to pass. And previous winners had lost twice and they have won, which is incredible," she added.
"I take it as a final, honestly, every point, every game, every set."
Her match against the 20-year-old Ostapenko was punctuated by plenty of booming winners and Muguruza was delighted to get the job done after the Latvian battled back from 5-1 down in the second set to almost reach parity.
"I wanted to win so badly and she was just not giving me anything," Muguruza added after sealing victory on her third match point.
"I think she was playing incredible shots but she was down. And, you know, I thought it's normal that she's playing incredible and I'd kind of wait for my moment, where until I serve and try to take control. It went well.
"I think Ostapenko had an incredible run this year and she has the confidence. That's what makes her even more dangerous. I knew going into the match that she could play unbelievable, so I kind of went prepared."
The Latvian was naturally disappointed to lose her first ever WTA Finals match but remains hopeful of improving against the other White Group players -- Karolina Pliskova and Venus Williams.
"The first match is always one of the toughest matches, and I think it's a great opportunity to play two more matches," she said. "If I play well in those two matches, I can still continue the tournament." (Editing by Clare Fallon)
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