Shortly after breakfast on September 19, 2015, a fresh summer-into-autumn Saturday in Brighton, the national rugby union team of Japan forsook the comfort of their Victorian seafront hotel for a gentle warm-up on the promenade.

Running through line-out drills on a basketball court was one way of focusing minds on the gargantuan task facing the team later that day, while stealthily introducing a little levity.

The sights, the smells, the sounds of the coast: ideal for untangling any ravelled minds. Staring out to sea, to their right stood Brighton's weather and fire-ravaged West Pier, evocatively skeletal; to their left, the iconic, bustling Palace Pier. Breathe in the sea air, feed all the senses, climb highest to grab a ball or two. The purpose was to be uplifted, in more than one sense. Japan were getting ready to put on their game face.

Handfuls of passers-by observed the group, decked out in red, black and white training garb, and a handful of those handfuls twigged the purpose of this limbering up.

From mid-morning beachside curiosities to global headline-makers by tea time, this is the story of the greatest upset in the history of the Rugby World Cup.

High hopes for Springboks

South Africa arrived at Heathrow on flights SA234 and SA236 on September 12, decked out in green and gold blazers, targeting a record-equalling third World Cup triumph. Their form had been shaky, with close losses to Australia and New Zealand followed by a head-scratching defeat to Argentina that saw them finish bottom of the Rugby Championship. Critics at home had their say, but the prevailing wisdom was that the Springboks would get it right when it mattered most. Only hosts England and the All Blacks were ahead of Heyneke Meyer's troops in the betting. Arriving by bus at their base in Eastbourne, they were received as heroes by locals and travelling Boks fans. A problem with seagull faeces at their training facility had been resolved, apparently, thanks to a groundsman and a hired-help hawk. All was well.

Eddie's swan song?

Japan were crudely characterised as rugby no-hopers in some quarters, but they had been in England for almost a fortnight by the time the Boks touched down, and reputedly together for around 120 days in camp before then. Eddie Jones, their former Australia coach, was not taking the job lightly. After all, he intended it to be his final hurrah to the international game. In the months leading up to the big day in Brighton, Japan had beaten Georgia, Canada and Uruguay, yet they had lost to Tonga, Fiji and the United States. They also struck a blow against South Africa six years earlier, when the International Rugby Board chose them above the 1995 and 2007 World Cup winners to stage the 2019 tournament. Japan were quietly confident of causing a shock or two during their stay in England, not that anybody outside their camp expected it to come on day two of the tournament.

The scene

The Falmer Stadium had hosted Brighton and Hove Albion football matches for four years, and the pristine new-build was controversially selected ahead of traditional rugby grounds such as Leicester's Welford Road to stage World Cup games. If there was a certain unfamiliarity, South Africa and Japan were in the same boat and the Springboks kicked off as 1/500 favourites to win the match. Moments before referee Jerome Garces' first whistle, those same line-out routines practised on the seafront were being repeated by the Brave Blossoms. Japanese fans had arrived from across the globe, but so too thousands in green and gold. Among their huge number was Ron Rutland, a former banker who had cycled from Cape Town, across Africa and Europe, to back the Boks.

What happened next will forever take some explaining. The Cape Times' correspondent Mike Greenaway, in his match preview, had invited Meyer's men to deliver an "emphatic opening statement", reasoning that "a good 50-point hiding will best announce that the Boks mean business". One UK news organisation, anticipating a routine South Africa win, despatched a reporter who had never covered a rugby game before.

The match

How the contest to-and-froed, South Africa four tries to two ahead but only tied at 29-29 with 10 minutes to play after dishing up a slew of penalties. Ayumu Goromaru feasted on their shambolic charity, his 24-point haul including a try, and even when Handre Pollard booted a penalty in the 73rd minute to nudge the Springboks in front, there remained a sense that history was in the offing.

Japan, pushing for the line and a man to the good after Coenie Oosthuizen's sin-binning, drove for glory with a minute left but could not ground the ball, the television match official making the call for an unsighted Garces. Chance gone? Not quite yet, not for these men with local sea air still lining their lungs. Japan almost scored in the right corner when captain Michael Leitch was blocked off just short. Those few dozen promenade gawkers had been replaced by 30,000 rapt rugby fans at close quarters, millions watching from home.

Then: Japan's finest rugby moment. Yu Tamura collected the ball from the ruck, and suddenly it was game on, a race to the opposite corner. Three perfect passes was all it called for, a relay with the rugby ball as its baton. It switched first from the hands of Tamura to Harumichi Tatekawa, and as the crowd roared Tatekawa fed Amanaki Mafi. One more successful pass and Japan would be home. Mafi offloaded and it was all down to Karne Hesketh, a New Zealander by birth, who had only come off the bench in the 79th minute. The former Otago wing gathered cleanly and charged for the line, defying JP Pietersen's desperate last-ditch tackle to dot down by the left flag pole.

The scoreboard showed Japan led 34-32, with time up.

Cue bedlam. Cue tears. Cue disbelief.

'Rugby at its finest'

"It's quite unbelievable," said Jones. "We always thought we could compete well today but to actually beat South Africa is a fantastic achievement for the team. If you're a young kid at home in Japan watching rugby now you'd want to play rugby at the next World Cup, so it's a fantastic thing for Japanese rugby."

Rutland, who would have been forgiven for being the most disappointed man on two wheels, tweeted it had been "a privilege to have witnessed such history on the pitch, and such amazing scenes between Bok and Japanese fans off it; rugby at its finest".

Joost van der Westhuizen and Chester Williams, both World Cup winners with the Boks, were among the disbelieving South Africans in Brighton. Four years later, neither man is still with us as another World Cup dawns, Van der Westhuizen succumbing to motor neurone disease in 2017 and Williams dying just two weeks ago.

Party time

Back at the Hilton Brighton Metropole on Japan's big night, a red carpet was rolled out to welcome back the heroes of the hour. Team liaison officer Jackie Takahashi later said "lots and lots of drinks" were consumed that evening at the hotel bar. One local reported 200 pints of beer being ordered by the team in a fell swoop. It was a night for such stories, and it hardly mattered whether any were embellished. The next morning, any hangovers were washed away by a squad dip in the sea.

No way Bok?

South Africa were at the lowest of low ebbs yet somehow they pulled themselves together to top Pool B before beating Wales 23-19 in the quarter-finals and losing only 20-18 to New Zealand in the semi-finals. Neither match lives so vividly in the memory as their horror show in Brighton, though. Japan lost their second pool match to Scotland but then saw off Samoa and the USA, cruelly missing out on a quarter-final place by two bonus points.

Pain plus time equals comedy?

This age-old theory does not yet apply to the Springboks, who continue to feel the wounds inflicted on England's south coast.

Bryan Habana, who played on the wing in that losing side, told Omnisport on the eve of the 2019 World Cup: "That day back in 2015 in Brighton, obviously from a South African perspective it was probably one of the darkest days in our history.

"Taking nothing away from Japan, but I think the manner in which we let ourselves down, our team-mates down, the jersey down and the country down was pretty disappointing. And mentally a massive challenge to get over."

He added: "Japan were incredibly well orchestrated through Eddie Jones and sort of got one over us by the mere fact that they were the better side on the day. They used their opportunities better and we were just poor in different facets of the game, which was not ideal, and not a memory I like to open up quite often about."

Japan's against-all-odds triumph may still be a hard-watch for South Africans but it inevitably became a film, with 'The Brighton Miracle' released this month: just don't expect to see it playing in too many Johannesburg or Cape Town movie theatres.

Shift in expectation

Japan were widely unfancied four years ago, but there has been an inevitable raising of the bar in expectation levels as they prepare to host this year's World Cup, even if the inspirational Jones is leading England these days. The Brave Blossoms won the recent Pacific Nations Cup after beating Fiji, Tonga and the USA, but a 41-7 seeing-to by South Africa - of all teams - on September 6 was a reminder they remain a second-tier outfit in global terms.

Reaching the quarter-finals this time is an obvious target, but head coach Jamie Joseph will probably need his team to beat Scotland or Ireland to do so.

Goromaru, who retired after his heroics in England, told World Rugby in September: "After the last Rugby World Cup the number of people interested in rugby in Japan increased dramatically. Before I left for the Rugby World Cup, no one had paid attention to rugby. Hosting Rugby World Cup 2019 in Japan for me, not as a player but as a fan of Japanese rugby ... it will be amazing."

He will always have Brighton, and the famous afternoon that gave Japan a taste for success on the global stage. The current crop long to experience such euphoria, this time in front of a home crowd.

Eight of the 23 players from the Brave Blossoms squad that took down the Boks, including captain Leitch, were due to be involved against Russia in Japan's tournament-opening game this time.

"Everyone understands how important this event is going to be, but none more than our staff and the players themselves," said coach Joseph. "We want to make everyone proud and we will be doing our best to make sure that happens."