Osaka overcame a shaky first set to log a dominating performance in the two that followed: 3-6, 6-3, 6-2 in just under two hours, Xinhua news reported.
Osaka came into the final on a nine-match winning streak stretching back to Toray Pan Pacific Open last month, winning four of her five matches here in Beijing in straight sets. Barty, by contrast, had needed deciders in all but one of her appearances.
Both players kept things fairly tight at the outset, holding their opening service games to love. The only player giving anything was Osaka, who tripped up with several netted unforced errors off the forehand side, including one that gave away a breakpoint at 2-all.
Osaka's 14 unforced errors to Barty's nine in the opener did not seem like a huge difference, but they were enough to give an in-form Barty the space she needed to find winners with both her forehand crosscourt and the occasional backhand slice. Ultimately, it would be a crosscourt lob sent too deep by Osaka that helped the Australian fight her to deuce and get the only break of the first set to go 4-2.
Barty would go on to serve out the rest of the set to claim the opener in just over half an hour. Barty, who fired off four aces in the first set, was also helped along the way by three double faults from Osaka.
The second set was an inversion of the first, both in terms of the score line and which player managed to stay clutch at key points.
Osaka found her form on service in the second, taking 86 percent of her first service points. She held to love on her first service and never faced break point for the entirety of the second set, and got the crucial break she needed to go up 4-2 before serving it out to force a decider.
Barty's forehand in particular, indisputably one of her best shots when it is finding its mark, slipped in the second set. She committed eight unforced errors on this side and only managed to find four winners with it.
Osaka broke at the outset of the decider to go one up, and she would keep things fairly clutch for the remainder of the set, breaking again to go up 5-2. Barty fought her to deuce when she served for the match, but her forehand kept giving her grief to the end. She lobbed a forehand crosscourt shot far off the mark to hand it to Osaka.
Barty committed 11 errors in the opening four games of the decider alone, and she would continue coughing them up, particularly on the forehand side where she had a tendency to send shots down the line when her crosscourt with topspin had been giving Osaka more trouble. In the end, she committed 20 of her 43 total unforced in the third set.
Along with the trophy, Osaka takes home $1,523,265 in prize money along with 1,000 WTA ranking points. Barty will have to settle for a mere $762,265 and 650 ranking points.