And it seems South African fans in Brighton, where the match was played, accepted defeat with good grace.
"People in Bok jerseys are coming out of restaurants to wave at the Japan team bus as it drives through Brighton. Rugby fans are amazing," tweeted Elma Smit.
Fans at other world cup venues also greeted the result with excitement.
"Huge ovation at Twickenham as Japan's winning try is shown on the big screen," tweeted Sonja McLaughlan.
So often bullied by rugby's heavyweights, Japan got off the canvas and lifted South Africa off its feet with a huge uppercut that sent shockwaves through the sport.
The players were still coming to grips with the achievement on England's sunny south coast.
"I can't believe it," loose forward Hendrik Tui said. "We're going to go back to the hotel, and have a few beers. We are still floating on air."
Ever the pragmatist, team coach Eddie Jones put into perspective what this will mean in Japan, where football heroes such as Keisuke Honda and, before him, Hidetoshi Nakata, have got used to sharing the sporting headlines with baseball stars.
Rugby has always been a niche sport, but Jones hopes this result will cause an upsurge in popularity.
"Now history has changed for Japanese rugby," he said. "Now we'll have kids back home who wanted to be baseball or soccer players -- like Keisuke Honda, or like Nakata -- who want to be the next Gorumaru."
Image 1 of 10: Ayumu Goromaru of Japan tackles Jean De Villiers of South Africa. Photo / Getty Images
Honda, with his dashing looks and peroxide-blond hair, plays for Italian side AC Milan and is a superstar. Before him, Nakata became the face of football in Asia in the late 1990s and early 2000s after making his name in the Serie A with Roma and Parma.
If any rugby player deserves to become a household name in Tokyo, then it's fullback Ayumu Goromaru. Quite simply, he produced the game of his life.
Marlon Gerbes shared this image with the caption 'My best mate scored the winning try! Was there to witness it. Proud as hell right now!' Photo / Via Marlon Gerbes Facebook
Japan's surprise win had everybody celebrating, including ground officials and stadium security. Photo / via Facebook
He was full of panache, daring running, thrilling risk-taking, and incredibly precise kicking. Performing under massive pressure, he nailed a superb conversion to level the scores to make it 29-29 -- and that was from his own try.
Added to that, he kicked five penalties in an atmosphere that was electric. When his try came late on at Brighton's Community Stadium, bringing Japan back into the match, the crowd's cheers almost lifted the roof off.
Dead-pan Jones joked: "I'm getting too old for this, 55."
South Africa contained World Cup winners from 2007, seasoned campaigners such as No. 8 Schalk Burger and lock Victor Matfield, who have seen it all before.
Japan blew them away.
Matfield's head gear was lopsided and twisted from a scrap he surely never expected, and captain Jean de Villiers' face was pockmarked and bruised from the ferocity of Japan's attacks.
Japan came of age, led by an uncrushable spirit, roared on by some fans who had waited 24 years to see the country's second ever win in the Rugby World Cup.
Next up, Scotland on Thursday in Gloucester -- which should brace itself for a red-and-white invasion.
