The 27-year-old fulltime horsewoman yesterday won the $200,000 Olympic Cup, backing up her win in the $50,000 Silver Fern Stakes on Friday night.
Twice at the weekend, Hay went head-to-head with Katie Laurie (Mystery Creek), the golden girl of New Zealand showjumping, and won.
She has always backed Centavos as a champion.
''I know he is a brilliant horse and is always capable of a win,'' she said of the stallion she imported from Germany as a rather inexperienced 3-year-old.
Hay headed home a quality 17-strong field to take the win in the Olympic Cup. Included in the line-up were previous winners Laurie and Maurice Beatson (Dannevirke), alongside other quality international riders Daniel Meech (Clevedon) and Helen McNaught-McFarlane (Taupo).
The quietly-spoken Hay was rapt.
''This has been our target for the show,'' she said.
''It is just incredible. I can't believe it.
''Centavos has a fantastic temperament and gives 100% every time he goes out.''
Hay, who also won the award for leading rider of the show, felt the Gerrit Beker-designed course was challenging and technical, but very fair.
Four combinations went clear in the first round - Amanda Wilson and Showtym Cassanova (Hikurangi), Hay, former Olympian Meech on Queen of Dance WS and McNaught-McFarlane on Carnutelabryere (Taupo).
Those with 12 faults or fewer came back for the second round in which five-time winner Laurie went clear on Dunstan Springfield. Beatson and My Gollywog picked up a time fault to finish on nine faults.
Hay also jumped clear but had a time fault to sit on one fault, while Laurie and Dunstan Breeze were clear to sit on eight, and McNaught-McFarlane had a rail down for four faults.
Hay is the first South Islander to win the cup since the 1970s. She does not train with anyone. Instead her parents, Vicki and Peter, help her.
But the future is a little up in the air for this talented rider.
''There's a lot of interest in Centavous both as a competitor and a stallion. He has a lot of babies on the ground, and some are doing particularly well.''
His progeny took the quinella in the Five-Year-Old of the Year class, with Clarke Johnstone (Matangi) on In Disguise taking the title and Oliver Edgecombe (Waipukurau) on Double J Escape second. Both have also won other national titles.
''They are doing really well, which is so encouraging.''
The family is looking to move to the North Island which Hay hopes will offer more opportunities for her as a producer of young horses.
Former Outram rider Clarke Johnstone (Matangi) brought Orient Express (16), his bronze-medal-winning world championship team horse, out of retirement to win the CIC2 title.
