Radwanska built a 6-2, 2-0 lead in a battle of former second-ranked players before Kvitova won eight of the next 10 games to take the second set and open a 2-0 lead in the third. Radwanska rallied to tie the deciding set 3-3 before reeling off three straight games to close out the match.
It was an unlikely triumph for Radwanska, who was three spots out of even qualifying for the event after the U.S. Open. She entered the WTA Finals as the No. 5 seed, but promptly dropped her first two matches of round robin play and needed help in additional to beating Simona Halep just to advance to the semifinals. Radwanska then beat rising star Garbine Muguruza in three sets Saturday to reach the finals.
"A few weeks ago I didn't even know I'd have a chance to be here, and there you go. It's just an incredible day for me," Radwanska said on-court after the match. "It means everything. It couldn't be any better. I think that was the biggest day in my life."
It marked the first title for Radwanska in any of the five biggest events on the WTA Tour - the four majors and the WTA Finals.
"It's incredible. I feel like it was a perfect day," Hingis told reporters. "The energy was a bit better in practice and Sania just played out of her mind - she was everywhere today - on her side, behind me - it's about choosing the right partner!"
Hingis and Mirza have won nine WTA titles since teaming up in the spring and earning the nickname "Santina."
"We feel very fortunate," Mirza said. "We've done some amazing things together and it's the perfect way to end the year for us."