Sunday’s Grand National Hurdle (4200m) at Sandown was billed as a match race between topweights Saunter Boy and Kiwi raider The Cossack, but the race proved to be anything but.

The 71kg impost didn’t prove a problem for the former, scoring a three-quarter of a length victory over St Arnicca, while New Zealand’s top jumper finished a further 20 lengths away in fifth.

Trainer Paul Nelson was perplexed with The Cossack’s subpar performance and couldn’t put his finger on what went wrong for the gelding who had won his previous three races in his homeland.

“We were very disappointed. We thought he would have been competitive, but it wasn’t his day,” said Nelson, who also part-owns the nine-year-old.

Nelson didn’t believe the firmer track (Soft6) than regular New Zealand winter footing was a factor for his gelding and having carried 73kg in two of his last three starts, weight was also an unlikely issue.

“I don’t think so (the track being too good for him). He hadn’t run for a month but I thought we had done enough with him to have him right for the run,” Nelson said.

“It was plenty of weight, but he carried 73kg earlier on in the year so he should have been up to it.”

The Cossack underwent a veterinary examination following the race, which came back clear.

“He pulled up fine. They vet checked him and he was good and he recovered really quick, so it was a bit of a mystery really,” Nelson said.

The son of Mastercraftsman is currently under the watchful eye of expat Kiwi trainer and former top jumps jockey Craig Thornton and Nelson said he will rely on his feedback when making a decision on whether they press on to the Grand National Steeplechase (4500m) at Ballarat later this month.

“We will see how he is in the next few days and have a rethink,” Nelson said.

“He is with Craig Thornton and Craig is very qualified to give us a sound report on him. We are considering the steeplechase in three weeks’ time.”

The Cossack has been a dominant force in the New Zealand jumping scene over the last few seasons, unplaced in just one of his 15 jumping starts. He remains undefeated in steeplechase events, having won the Ken And Roger Browne Memorial Steeplechase (3900m) two starts back.