Auckland: Unseeded Zheng Jie claimed her fourth career singles title and her first since 2006 when Flavia Pennetta was forced to retire injured in the third set of Sunday's ASB Classic final.
The 28-year-old Zheng was leading 2-6, 6-3, 2-0 when fourth-seeded Pennetta, who required courtside treatment to a back injury, indicated she was unable to continue.
It was Zheng's first title since 2006 at Estoril and the Chinese now has four titles from six final appearances.
Italy's Pennetta, who was bidding for a 10th career singles title, finished runner-up in Auckland for the second time, having also reached the final in 2010.
Pennetta had not dropped a set in reaching the final and looked in similarly commanding form Sunday when she took the first set in 46 minutes.
Both players saved breakpoints in their opening service games but Pennetta took charge when she broke Zheng to love in the third game, then rallied from 0-40 down on her own serve to lead 3-1. She broke again for 5-2 and served out the set at her first opportunity.
Pennetta broke Zheng in the opening game of the second set and seemed on course for a convincing win. But she began to look uncomfortable, particularly when serving, and was forced three times to call for medical treatment.
Zheng recognized her opportunity and began to play more aggressively, stepping into the court to take the serve earlier and making use of her strong, whippy forehand.
She broke back in the fourth game of the second set and gained a decisive break in the sixth game, and took the set in 42 minutes.
Pennetta dropped serve in the opening game of the third set and, after battling through the second game, elected to retire. The world No. 20 now heads to Melbourne for the Australian Open which starts Jan. 16.
"I'm still quite happy. It's been a good week for me and a good way to start the year," Pennetta said.
The singles final, scheduled for Saturday, was postponed until Sunday and then moved indoors because of rain.