A week after winning in Auckland, Radwanska reinforced her billing as the top-seeded player in Sydney when she claimed her 12th career WTA title and her ninth straight match to start the 2013 season.
Radwanska faces Australian qualifier Bojana Bobusic in the opening round of the Australian Open next week.
Last year's runner-up, Benneteau edged Anderson by the solitary point to claim the 32nd and last seeding at next week's Australian Open after Anderson passed up the chance to earn ranking points by representing South Africa at the Hopman Cup.
Anderson had a small revenge on Friday when he beat Benneteau in a thrilling match of almost 2½ hours.
Tomic, known for his volatile temperament, showed fortitude in overcoming heat stress caused by 104 degree temperatures to beat Seppi for his seventh straight win.
Ranked 36th, Anderson played his way into his fourth tour final and remained on course for his third title, rallying from a set down to beat the 35th-ranked Benneteau.
Benneteau broke Anderson's powerful serve twice, in the fifth and ninth games, while dominating on his own serve to take the first set.
Anderson fought back behind his improved serve to take the second set, serving four aces and adding nine clean winners to reclaim the initiative.
Little separated the players in the final set and both gave up their serve once before heading into a tiebreaker. The tiebreak went back and forth for 19 points before Anderson clinched victory with an overhead winner.
Tomic complained of dizziness during the first set and had to call for attention from the tour trainer while leading 5-4.
He fended off four set points in the tiebreaker before snatching the first set in 55 minutes when Seppi played a forehand into the net.
Seppi, who led Novak Djokovic by two sets at last year's French Open, gave up the second set when he dropped serve in the ninth game. Tomic took a 5-4 lead and made no mistakes in serving out the match in 1 hour, 23 minutes.