Costello, of Mangawhai Heads VLS, backed up her 2012 victory by taking out the women's division, using her local knowledge in the final to pick off one of the biggest waves.
Double finalist Brenna Bishop, of Karekare, also put on a good show placing third behind local surfer Alana Thrasyvoulou.
It was a similar affair in the juniors with Te Arai surfer McRae, also of Mangawhai Heads VLS, picked up his second consecutive junior title.
With a strong focus on traditional longboarding, including nose rides and fancy footwork, the draw took over nine hours to complete.
Paul Steinberg, of Santa Cruz, USA, stole the show in both the open men's and classic divisions with some stylish traditional surfing.
Steinberg, who came to New Zealand as part of the California Lifeguard Exchange, rode an old Peter Way board that was made circa 1960 in both divisions and linked a number of long, critical nose rides with switch foot and soul arch turns.
Other stand-out surfers in the Open included local Neil McInnes with his polished forehand and Whangamata styler Andrew Earl-Peacock.
Auckland's Dave Sneyd claimed his maiden victory in the master's division, and the smooth natural footer was a popular victor in the division.
Lifeguard Longboard Nationals:
Open: Steinberg, USA, 1; McInnes, Mangawhai Heads, 2; Andrew Ear-Peacock, Whangamata, 3; Toby Gibb, Mangawhai Heads, 4.
Classic: Steinberg, USA, 1; Tai Flavell, Mangawhai Heads, 2; Andrew Ear-Peacock, Whangamata, 3.
Women's: Costello, Mangawhai Heads, 1; Alana Thrasyvoulou, Mangawhai Heads, 2; Brenna Bishop, Bethells Beach, 3.
Juniors: McRae, Mangawhai Heads, 1; Brenna Bishop, Bethells Beach, 2; Daniel Hessell, Mangawhai Heads, 3.
Masters: Sneyd, Auckland, 1; Steve Jones, Omaha, 2; Graham Darlow, Mangawhai Heads, 3; Bob McDonald, 4.
