The win cements an impressive year for the Danish star which saw her win her first Grand Slam title at the Australian Open, returning her to the world number one position exactly six years after last holding the top spot.
Wozniacki told the WTA official website: "I didn't feel great going into the tournament, to be honest".
"I wasn't able to play with that fire that I have in all my matches", Del Potro added, saying however that 34th-ranked Basilashvili "played unbelievable".
In the final match, Wozniacki held the opening set with a smash.
This was her third trophy of the season and 30th title of her career.
Basilashvili won 6-4, 6-4 to cause an upset against the world number four at Beijing's National Tennis Centre in China's capital. "She didn't give me any presents, it was tough", said Sevastova. Then I started believing that, you know, I'm really hitting my form, playing myself into shape.
After that it was a story of mistakes by world number 12 Nishikori - 11 unforced errors in the first set - and consistent serving by Medvedev who strolled to a 6-2 first set in just 25 minutes. She sealed the win on her own serve and admits her game is now in a good place.
The 20th-ranked Latvian will face the victor of the semifinal between China's Wang Qiang and Caroline Wozniacki of Denmark.