It was a tale of two halves for Canada's men's rugby team on Sunday.

Up against Japan to open the Pacific Nations Cup tournament, Canada faltered early. Thirty-one minutes into the game, the Brave Blossoms held a 31-0 lead.

"(Japan) were so efficient, the speed of ball," said Canada's head coach Kingsley Jones. "It was like a whirlwind, like a wave coming over the players."

The Canadians rallied but couldn't climb out of the hole, and ultimately settled for a 55-28 loss.

"I spoke at halftime to the team and I said `Do we want to wait until next week to put things right or do we want to start now? Can we win the second half?' That was the challenge," Jones said.

"And we won the second half. Japan may have taken their foot off the gas a little bit, but I'm really proud of the players, the way they stuck at it."

Warner Dearns touched twice for 14th-ranked Japan, while Malo Tuitama, Dylan Riley, Kani Shimokawa, Seungsin Lee and Tomoki Osada also contributed tries. Lee also booted six conversions and a penalty.

Andrew Coe, Lucas Rumball and twins Talon and Takoda McMullin each had a try for No. 21-ranked Canada, while Peter Nelson added four conversions.

Japan jumped out to an early lead when Tuitama broke through the Canadian line and ran in for a try just four minutes into the game.

Canada's offence responded, working its way deep into scoring territory, but were unable to finish.

"I think I'm disappointed in that first 25, 30 minutes. I don't think we did ourselves justice for where we're at," said Rumball, Canada's captain.

"(Japan) came in with an around the corner speed kind of game, and we didn't adjust quick enough. I thought after that, we found our feet, found our bearing, and got into the game better. But we can't strive to be a good nation and strive to win games and start like that."

The Canadians finally got on the board before the half thanks to a loose ball booted by Jason Higgins. Coe chased it down and leapt on top of it for a try and Nelson made the ensuing convert, cutting Canada's deficit to 38-7.

Japan's offensive outburst continued early in the second half. Three minutes in, Dearns handed off to a teammate who was taken down by Canada's Cooper Coats just ahead of the line. Lee collected the ball and manoeuvered around the mass for a try.

Canada responded with a gritty effort at the other end of the field. After grinding through an extended series of rucks on the line, Rumball touched. Nelson booted the convert and shrunk Japan's advantage to 45-14 at the 46-minute mark.

The home side scored again four minutes later off a line out. Andrew Quattrin handed off to Talon McMullin, who evaded a Japanese defender and rushed in to touch before Nelson added another convert.

His brother added to the score line on an advantage in the 80th minute. Nelson booted the ball and Takoda McMullin got a hand on it for the try.

Asked who made the better play, Talon McMullin demurred.

"I've heard both. I'll give it to him," he said with a grin. "I think the finish was better from him. That's a pretty unreal way to score your first try."

The 22-year-old twins from White Rock, B.C., had dozens of friends, family members and teammates from both high school and the University of B.C. rooting for them in the stands on Sunday.

"We've always been able to play together, but then to be able to play on the top stage together, we're always just happy together," Talon McMullin said. "We'll fight here and there, but once we step on the field, it's nothing but love with him. He scores, I celebrate the most. I score, he celebrates the most."

The Canadians will continue the tournament in Carson, Cali., on Aug. 31 when they face the United States.

Both sides will head to Japan for the semifinals and fifth-place game in Tokyo on Sept. 14 and 15. The championship game and third-place matchup are set to go Sept. 21 in Osaka.