The Russian, 25, lost four match points in the second set tiebreak but came back in the third to win 6-4 6-7 6-3.
Her first title in 10 months pushes her to 14 in the world rankings ahead of the US Open, which starts on 30 August.
“It was very hard to close and I choked for first time in my life,” said the two-time Grand Slam champion.
Kuznetsova double-faulted on two of her four match points during a second set tiebreak where she squandered leads of 4-0 and 6-3 to allow Radwanska back into the match.
After falling behind 2-1 at the start of the third set, Kuznetsova grabbed control of the match from just inside the baseline with a series of winners before securing the title with a backhand down the line.
“My knees were shaking and I couldn’t push on my serve and now I know why people double fault on match points,” added Kuznetsova.
“I just shook. The trophy was very important to me. I was very embarrassed and I just got it back together and dictated.
“To play that bad at end of the second set and then to let her come back and see me choke, I had to be twice as strong in the third set and I was.
“It’s pretty funny now that I won the match, but if I lost I might be thinking: ‘should I finish playing tennis?’ I doubt it will happen again.”