Halep lost to Ostapenko in this year's French Open final but gained revenge with a superb display in Beijing that took just 75 minutes.
She was always in control against the world number eight Ostapenko and put herself on the way to victory when she broke the talented 20-year-old in the first game of the first set.
"Maybe first time on court (to cry) nice tears".
Romanian Halep, 26, beat her French Open conquerer 6-2 6-2 in Beijing. "I changed tactics and worked pretty well".
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That has consequences for Great Britain's Johanna Konta, who is battling Garcia for the last spot at the WTA Finals.
The outstanding Williams is temporarily out of tennis after having her first child.
A year ago the 22-year-old was suspended by tennis authorities for his behaviour in a defeat in Shanghai during which he appeared to give up and argued with the crowd.
"I think she played an incredible match, probably the best she's played against me in all of our previous meetings", she said.
Kyrgios's exuberance won favour with the crowd in the Chinese capital and after winning one thrilling rally he turned to the spectators and gestured with flailing arms for them to keep roaring him on.
After Halep had broken for a 3-2 lead in Saturday's second set, Ostapenko briefly found top form, immediately getting back on level terms before holding confidently.