The TAB had Costume at the odds of better than 50-1.
Debbie labelled her horse, with Michael Coleman in the saddle, the "favourite one" after she clocked 2m 2.66s.
"She's won a group 1 in autumn and she won one today so she's a special mare."
Debbie no doubt relished having Costume come in as an underdog.
"I suppose the pressure's off when you're not the favourites."
Costume went through almost unnoticed, seldom getting a mention on the loudspeaker through the 2040m good track.
"She just had to find her mojo and get back on our A game today," Debbie said.
The No 4 barrier was "nice" although Costume had a penchant for getting back on the field and having the ability to draw from anywhere.
"It was a superb ride by Michael Coleman and he knows the mare backwards so it was just a great get up to win today," she said of the Matamata jockey who was born in Hastings but moved when he was five with father Peter to Masterton where the senior Coleman worked as trainer for Costume's owner, Garry Chittick.
Son and stud principal Mark Chittick is a part-owner and co-breeder of I Do, who won the first leg of the spring carnival, the Makfi Challenge Stakes.
The Tuhikaramea couple's Soriano, from barrier 3 with apprentice jockey Rory Hutchings, finished third by a long head in front of Zonza and Leith Innes.
The win on Saturday on Costume was Michael Coleman's fourth classic victory in Hastings.
His father, also living in Matamata, was in the Hylton Smith Members' Stand to watch him fist the air in jubilation.
The jockey won his first Hastings classic in 1977 on Moss Downs.
The next one came in 2005 on board Xcellent. Five years later he crossed the line first on Wall Street.
"It's pretty happy times," Coleman said, echoing the sentiments of Debbie that the pressure of disappointing anyone had they not prevailed was a given.
Costume, he revealed, was served by stallion Pins last week which did the trick, after two not so convincing runs, including the Windsor Park Plate (mile) where she needed to find a couple more lengths. That changed on Saturday.
"She made a great run from 700 metres and then another into the clear so she's got the job done."
On the way to the races, Coleman spotted snow on the Napier-Taupo Rd but on arrival voted the day "refreshing" in the Bay.
It was the second win for the Waikato Stud Ltd. Its other classic winner was Legs in 2006 with jockey Lisa Cropp.
It was the Rogersons' seventh group 1 victory.
"It's special but others have also been special," Debbie said, singling out Katie Lee's two group 1 wins as "very special".
Filly Katie Lee became the first horse in New Zealand history to win the 1000 and 2000 Guineas, in 2009.
Costume will now be bracketed for an age-for-weight group 1 race next month.
"She's a petite filly but has a big heart," she said.
