Ireland is in mourning after one of the biggest upsets in Rugby World Cup history shattered their dreams of winning the tournament.

While the World No.2 ranked side is still alive and could still realistically top the group with Scotland and Japan still to play each other, a sense of resignation has set in across the rugby mad country after the shock of losing to the Brave Blossoms.

In his column for the Irish Independent, Eamonn Sweeney makes the case that Ireland's 19-12 defeat to Japan was the worst defeat in the country's sporting history.

The headline sets the tone: "Can you think of a worse one?" it asks before glibly renaming a match that will go down in history from the 'Shizuoka Stunner' to the 'Shizuoka Shitshow'.

Citing some of the recent embarrassments in Ireland's rugby history, Sweeney wrote: "The mockery of Eddie O'Sullivan because his team only scraped past Georgia and the laughter which greeted the infamous draw in Liechtenstein seem a bit unfair now.

"The Shizuoka Shitshow is in a class of its own."

One of the all-time greats of Irish rugby, Brian O'Driscoll claimed on ITV's coverage of the game the "mood of the whole country has shifted in 80 minutes.

"For one, I didn't see that happening. I knew it would be a tough game playing against the host nation. They'd nothing to lose but huge credit to Japan, they played terrific rugby but Ireland looked very blunt.

"They looked devoid of ideas, they looked devoid of energy actually. I wonder did the conditions and the humidity take effect because it wasn't the Ireland we've come to expect over the last couple of years."

O'Driscoll's default setting in his analysis was to praise Japan and to temper his criticism of Ireland, which was oddly common following this defeat.

So much so, it prompted bemusement from Irish blogger Paul Hosford in a tweet that attracted more than 100 likes.

While the humidity was raised as one mitigating factor with the Irish players "sweating buckets in the warm up", the refereeing of Australian Angus Gardner was another, with his performance savaged by Irish Times reporter Gerry Thornley.

Just over a week ago Ireland were the No.1 ranked side in the world and they built towards that over the last couple of years on the strength of their ruck dominance but they were unable to assert themselves in that area against Japan.

"A big thing for Ireland over the last couple of years has been their ruck," said ITV panellist and Ireland rugby legend Paul O'Connell.

"They've had the best ruck in the world in terms of ball retention and in terms of speed of ball. And Japan has just absolutely done a job on them at the breakdown."

While O'Connell gave credit to Japan for disrupting Ireland's breakdown work effectively, Thornley gave a more cynical view, turning his attention to the referee.

"Ireland had profound problems at the breakdown and will feel a huge grievance over the awful performance of referee Angus Gardner, losing the penalty count 9-6, with most of the damage done at ruck time," he wrote.

"There Gardner was conned into giving Japan penalties when they held Irish players in, while allowing them all manner of largesse.

"All that said and done, Ireland really struggled to resource rucks and affect clearouts, not helped by the manner in which they increasingly lost collisions."

Ireland's loss leaves them on a collision course with the All Blacks in the quarter-final unless Scotland can rise from the canvas to beat Japan in their pool match, a result that would now be a significant upset.

While Ireland have beaten the all-conquering All Blacks in their recent history, the loss to Japan seemed a jarring reality check, with claims that they would be zombies walking in a haze towards certain elimination.

"Now Ireland have become the zombie team, condemned to trek on for another three weeks towards inevitable quarter-final defeat," wrote Sweeney in his column for the Irish Independent.

The irony of that sentiment, given all the chest beating that happened after winning matches that counted for far less; most recently their 16-9 win over New Zealand in Dublin last year, which was described as a 'friendly' by award-winning sportswriter Ewan MacKenna.