Ashleigh Barty received the prestigious Newcombe Honour for the third time.
World No.40 Mladenovic started slowly before taking advantage of an error-strewn Barty, whose 15-match Fed Cup winning streak was ended in a see-sawing match lasting two hours and 31 minutes.
Barty will play Caroline Garcia of France. Ajla Tomljanovic will make her debut for Australia playing the opening singles match Saturday against Kristina Mladenovic.
The title adds to the 23-year-old Australian's lengthy list of achievements in 2019 including winning her first Grand Slam title at the French Open.
Barty, like Svitolina, dropped the opening set of her semifinal before beating second-ranked Karolina Pliskova of Czech Republic 4-6, 6-2, 6-3.
Ashleigh Barty was the first Australian to win the French Open in 46 years and is now aiming to become the first Australian woman to end the season with the number one ranking since Margaret Court in 1973.
Andy Murray's impressive run in the China Open came to an end in the quarterfinals, but Naomi Osaka and Ashleigh Barty proceeded to the semis in the women's singles.
Previous year's champion Naomi Osaka, as well as World No.1 Ashleigh Barty will compete at US Open 2019.
Ashleigh Barty beat Julia Goerges to become the first Australian woman since Goolagong Cawley to seal number one spot in tennis rankings.
There still has not been a repeat champion this year among the men or women.
A little more than two years after switching back from bat to racket, Barty has caught the attention of a nation.
It was Halep's first match since October after a lengthy layoff due to a herniated disc in her back.