Irish visitor Blackstairmountain has claimed a famous success for trainer Willie Mullins and jockey Ruby Walsh in the Nakayama Grand Jump in Japan.

The eight-year-old was well beaten on his Tokyo debut when only ninth in the traditional lead-up, the Pegasus Jump, but he stepped up markedly on that form to land the world's richest steeplechase worth Y135 million ($A1.29 million).

A winner at the highest level at Leopardstown in December 2011, Blackstairmountain was up in distance to 4250 metres and was the only foreigner in the race.

Walsh was happy to sit in mid-division in the early stages of the race, steering a wide course before allowing Blackstairmountain to work his way into contention.

He had half a length to spare at the line, becoming the first European-trained winner of the race.

Mullins said he had had the Nakayama race in his sights for some time.

"I had the Nakayama Grand Jump in consideration back around 10 years ago," Mullins said.

"I had two good jumpers, Florida Pearl and Alexander Banquet - big winners back home - that were invited.

"But when I came out to check out on the conditions here, I decided it wouldn't suit both horses and withdrew the entry.

"I thought it would suit what we call a "summer horse" and it took me a few years to find a horse good enough.

"I had my doubts after Blackstairmountain's performance in the Pegasus but Ruby Walsh, the jockey, was more positive.

"I am thrilled and if the horse's condition is fit to come again next time, I would be quite eager to do so."

New Zealander St. Steven won the race in 2002 while Australian Karasi claimed an incredible three wins from 2005 to 2007 but Blackstairmountain was the first overseas horse to contest the race i four years.