Japan wing Karne Hesketh conceded his match-winning try against South Africa was beyond his imagination prior to Saturday's shock victory.

The global rugby community was stunned on Saturday when Japan upset the world number three Springboks 34-32 at the Rugby World Cup - with Eddie Jones' Japanese side having been rated 1000-1 outsiders prior to the match in Brighton.

Hesketh got on the end of a flowing move in the 84th minute to secure Japan's win - the first of their history over South Africa - and the New Zealand-born wing conceded even dreaming of such a moment seemed silly prior to it becoming reality.

"Before that game, just being involved in the World Cup was the pinnacle of my career," he said on Sunday.

"To be part of something like last night is so special.

"I could never imagine. I remember crossing the line and thinking, 'We've done it' - just immense happiness and pride, and to be lucky enough to be on the end of that, it was special."

Japan celebrated just their second World Cup victory with a team dinner and "a couple of beers" but Hesketh insisted he and his team-mates want to build on their early success.

Hesketh and Co. face Scotland on Wednesday, followed by Samoa on October 3 and United States on October 11.

"If we're mentally sharp, we'll be good," the 30-year-old said.

"It comes down to being prepared and doing everything as seriously as you can. And doing the off-field work too - studying your opposition, knowing your plays, what kind of stuff we want to do."

Hesketh added: "As much as we wanted to celebrate [on Saturday], it's not the only job we came to do."