Petkovic made quick work of her opponent, winning in a mere 61 minutes. She had her serve broken twice, but did not allow Niculescu to win a game on her own serve. Niculescu won just 11 of 40 points during her seven service games.
It's been a solid year for Petkovic, who opened the season with a runner-up finish to Petra Kvitova in Brisbane and won her second career title in Strasbourg the week before the French Open. She is 2-2 all-time in WTA finals.
Petkovic was the only woman to appear in three Grand Slam quarterfinals this year, reaching the round of eight at the Australian Open, French Open and U.S. Open. She's advanced to at least the quarterfinals in all but six of her 18 events this year.
"I've played really well this season," noted Petkovic. "I played very consistent and won a lot of matches. It's definitely special to be in this final."
Radwanska will be gunning for her seventh career title and third this year. She won in Carlsbad before the U.S. Open in August and captured last week's event in Tokyo, improving to 6-2 all-time in WTA finals.
It wasn't much of a contest on Saturday with Pennetta, who had taken out world No. 1 Caroline Wozniacki in the quarterfinals. Radwanska broke serve three times in the first set and added a pair of breaks in the second.
Sunday's final will mark the third meeting this year and the fifth overall matchup between Radwanska and Petkovic. Radwanska has won each of the previous four, including a semifinal triumph in Carlsbad and a quarterfinal win in Toronto earlier this season.
"We played two times against each other in the summer; I won both those matches," Radwanska stated. "That doesn't mean anything though. It's always very tough and very tight against Andrea. She's playing well. I have to play even better than today to beat her tomorrow."
The winner will not only pocket a first prize of $775,000, but will also move into the top-10. Radwanska is currently ranked 12th and Petkovic is 11th.