From a field of six nations, the hosts registered 454.698 points to finish more than 25 percentage points ahead of their nearest rivals from Canada on 428.708.

Spain lined up in third place on 414.421 points, followed by Denmark in fourth, Costa Rica in fifth and Australia in sixth.

"I'm extremely proud that the US won this Nations Cup again this year," said Robert Dover, the American Chef d’Equipe.

"Even more importantly, I was hoping for our riders to achieve personal bests and to do better than they have been doing this season, and with each class grow more confident as we head towards Europe and the Olympics."

The FEI Nations Cup format permits teams composing both big and small tour combinations, with big tour combinations receiving a 1.5 per cent bonus to their scores.

The move to allow both tours to compete was taken by the FEI in an effort to encourage participation and to help riders hone their skills and gain more experience.

Spain and Costa Rice were represented by small tour combinations at the Wellington fixture, while Australia, Canada and the US fielded big tour partnerships and Denmark entered a mixed team of small and big tour riders and horses.

America’s Laura Graves was the stand-out performer, posting personal best results in both yesterday’s Grand Prix and today’s Grand Prix Special.

Graves and her 14-year-old Dutch-bred Verdades secured the US victory with a score of 78.294 poinra in the Grand Prix Special.

This rose to 79.794 with the added 1.5 per cent bonus points.

"I couldn’t be more thrilled," Graves said after the two days of competition.

"It’s been a long season for us, and this is going to be a long competition."

US team-mate Kasey Perry-Glass also recorded a personal best with the 13-year-old gelding Goerklintgaards Dublet.

The first official FEI Nations Cup Dressage series is due to continue with legs in the Danish city of Odense and the French commune of Compiègne in May.