Spears Funabashi Tokyo Bay won their first-ever piece of silverware and became the second team to have their name inscribed on the Japan Rugby League One trophy as they beat Saitama Wild Knights 17-15 at Tokyo's National Stadium on Saturday.

A try by Haruto Kida and four penalties from Bernard Foley secured the win in front of 41,794 fans as Spears made the most of an error-filled performance from the defending champions.

Kida, who had been on the end of a crunching tackle from Marika Koroibete earlier in the game, was on hand to take an inch-perfect kick pass from man-of-the-match Harumichi Tatekawa in the 69th minute to score the all-important try.

Tries earlier in the half by Shota Horie and Tomoki Osada had seen Wild Knights take the lead for the first time. But a continuation of their errors and some dogged defense from Spears saw Frans Ludeke's men hold on for the win.

"Rugby is a game of pressure and finals are built on mistakes, and the team that takes advantage is always going to go all the way," said Spears lock Ruan Botha, who was at the heart of their forward effort.

With the platform laid by their pack, Foley, Tatekawa and Ryan Crotty then added the much-needed experience and composure in the backs, a point not lost on their coach.

"You could see with our kicking game. We applied pressure, and they really felt it," said Ludeke. "We showed for 80 minutes our game control."

Wild Knights coach Robbie Deans was quick to praise Spears for their win but admitted he was mystified by how his own side had performed.

"We did contribute to our own demise. On big occasions, you want to be at your best, but we weren't for some reason," Deans said. "As is the case in every competitive final, you need to take every opportunity. We had ample opportunities but did not take them. We lacked composure, and that hurts."

Ludeke, Deans' old coaching rival from their days in Super Rugby, said the win had been seven years in the making and was for everyone who had invested their time and money in Spears.

"It's a special feeling to win a final," Ludeke said. "We have kept growing as a team, believing and trusting and working hard ... and that's why today was such a special event."