The former top-ranked Davenport improved her record to 18-1 in singles since her return to the tour.
She gave birth last June to her first child, son Jagger.
Jagger Jonathan Leach, aged six months, was courtside on Saturday for his mother's victory, attended by his nanny, but seemed nonplussed by the occasion and cried volubly when first introduced to the crowd.
He was quickly calmed by Davenport and took an eager interest in proceedings, including the presentation of the USD 22,000 winner's cheque.
The win followed Davenport's tournament victories in Bali - achieved after a 51-week absence from the tour - and Quebec City and her semi-final appearance in Beijing.
The Quebec title was her 53rd, tying her at eighth place with Monica Seles on the all-time list of female title-winners. She now holds that place outright.
Davenport was playing in Auckland for the first time and will play no other tournaments before the first Grand Slam of the season, the Australian Open, starts on 14th January.
She will be bidding to win that title for the second time.
Davenport, No 234 on world rankings entering the Bali tournament, became the fourth lowest-ranked player in WTA Tour history to win a singles title.
The right-hander, who was last ranked No 1 in January 2006, re-entered the top-100 in November and was unseeded at Auckland on her entry ranking of 73. Rezai, 20, is ranked No 90, off a best ranking of 40 in January last year.
Rezai, counted Venus Williams and Marina Sharapova among her singles victims during the 2007 season.
She upset third-seeded Katarina Srebotnik en route to the Auckland final while Davenport beat compatriot Laura Granville, fifth-seeded Anabel Medina-Garrigues, Sara Errani and sixth-seeded Tamira Paszek.
She droppd only one set in four matches.
She won the first set today in 25 minutes, breaking Rezai in the second and eighth games and the second in 34 minutes, breaking in the fourth and eighth.
In winning, Davenport improved her percentage of wins in singles to 79.4 percent - 792 wins in 918 matches - which is the best winning percentage in WTA hisory.
"Hopefully, I'll still be playing in 2009 and if I am I'll definitely make this the first stop of the year," Davenport said.
Rezai contributed to her own defeat with a high percentage of unforced errors.
"Lindsay was playing well and she didn't give me time to play well," Rezai said.
"That's why the score is 6-2 6-2 and the game was so quick."
