* Russian wins 12th career title
* Defending champion Radwanksa outgunned in final (Adds quotes, detail)
TOKYO, Sept 29 (Reuters) - Russia's Nadia Petrova upset defending champion Agnieszka Radwanska 6-0 1-6 6-3 in the Pan Pacific Open final on Saturday to complete a sensational run at the Tokyo tournament.
It was the 30-year-old's second title of the year after winning a Wimbledon warm-up event in Den Bosch, the 12th and also most prestigious of her career.
"The first and third sets were perfect tennis from my side," Petrova told reporters after winning the WTA premier five event, which featured nine of the world's top 10 women.
"It's the biggest tournament I've ever won," added the Russian, who is set to rise from 18th in the world to 14th. "I never expected I would be in this position. It feels amazing."
Petrova inflicted the dreaded 'bagel' on third seed Radwanska in the first set, taking it with a blistering ace down the middle to rub salt in the wounds.
The Pole quickly turned the tables but Petrova produced some superb tennis in the decider, closing out proceedings with a drive volley before sinking to her knees in delight.
Petrova, who beat top 10 players Sara Errani and Samantha Stosur on her way to the final, enjoyed her best season in 2006 when she won five tournaments.
Winning the $2.16 million hardcourt event earned Petrova $385,000.
Radwanska, close to tears during her post-match speech, was left to rue two double-faults in a row which cost her the eighth game of the third set, and ultimately the match.
"I was pissed," said Radwanska, who furiously smashed her racquet on the court after gift-wrapping Petrova a 5-3 lead in the decider.
"It's always emotional in a final. It was a weird match, like a rollercoaster. That's women's tennis. You never know what is going to happen so you have to fight until the end." (Editing by Patrick Johnston)