Six-time series winner Katie Laurie, who flew in from Australia to compete in the final, retired after Breeze refused the first fence.
"She just didn't want to jump today," said Laurie. "It is a bit disappointing."
Those with 12 faults and less came back for the second round where Olphert added 10 to her tally, Morrison and Hayward both added eight, and Johnstone another four. It was down to the top three – Alfeld, Clark and Morrison.
Alfeld was all class to notch just the second clear of the class, despite a rather hairy change of line into the fourth fence. Clark took a rail at the bogey fence of the round to add four to hers and it was down to Morrison to go double clear and win the round.
But it wasn't to be as she took both the bogey fence and the last to add eight to her tally, giving the class to Alfeld.
Alfeld admitted to having a few nerves coming into the class but said once she walked the course she felt far more comfortable.
"It suited him so well. I had high hopes heading into the final but anything can happen. I just wanted to go out and do my best."
Her efforts today saw her also win the series by 14 points ahead of the second-placed Morrison, with Hayward in third, another nine points adrift. As the series winner, she also has the opportunity to represent New Zealand at the Longines FEI World Cup Final in Paris in April, but she said it was unlikely.
"I would love to go and watch though."
However, Alfeld does aspire to ride offshore – just not yet.
"I am a bit green I think! I am not sure it is my time just yet."
The only coaching Alfeld has had all season has been with her ESNZ Talent Development Squad training, but she is looking forward to some time with visiting Canadian trainer Jen Hamilton.
Sideline to watch her victory was mum – and My Super Nova's breeder – Lisa Alfeld.
"I am very proud," she said. "At the start of the season I didn't think it would end like this, but Rose was on a mission."
And she did it. My Super Nova was broken in by her husband, Murray, who with Rose, did the foundation work with the young horse. My Super Nova also won the prize for the best shod horse.
The New Zealand World Cup League started in October in Hawke's Bay with riders gathering points at the seven rounds with just their four best results to count.
Results:
Bayleys Real Estate FEI World Cup NZ League Final: Rose Alfeld (Leeston) My Super Nova 1, Clarke Johnstone (Matangi) Quainton Labyrinth 2, Samantha Morrison (Tauranga) Biarritz 3, Tess Clark (Gisborne) Sinatra II 4, Lucy Olphert (Tauranga) Eve Saint Laurent 5, Briar Burnett-Grant (Taupo) Fiber Fresh Veroana 6.
Bayleys Real Estate FEI World Cup NZ League Final Series: Rose Alfeld (Leeston) My Super Nova 87 points 1, Samantha Morrison (Tauranga) Biarritz 73 2, Emily Hayward (Te Awamutu) AP Ninja 64 3.