1991: Western Samoa beat Wales, 16-13
The Samoans had a point to prove after not being invited to the first World Cup in 1987. The Welsh had the misfortune to be standing in the way of that point.
Wales' defeat at Cardiff Arms Park marked the first time a leading rugby nation was beaten at the RWC by a team considered to be a rank outsider. We should have known better: the Samoans have made a habit of reaching the play-offs in subsequent World Cups, inflicting pain and humiliation on supposedly bigger nations along the way.
It was possibly the strongest lineup the Samoans have fielded with the likes of Stephen Bachop, To'o Vaega, Junior Paramore, Pat Lam, Frank Bunce, Peter Fatialofa and Apollo Perelini in their ranks. With two tries apiece, Mathew Vaea's kicking won the day.
"Thank heavens we weren't playing the whole of Samoa," one Welsh fan (allegedly) said as the shock of defeat sunk in.
1999: Samoa beat Wales, 38-31
Lightning strikes twice, and by 1999, the Welsh couldn't claim to have been unaware of the Samoan menace.
Graham Henry-coached Wales had won 10 on the trot and fancied revenge for the 1991 defeat. The islanders became the first visiting team to win at the Millennium Stadium as the Red Dragon officially became Samoa's bunny.
While the 1991 match was tense and dominated by forward power and kicking, this one was a feast of running rugby, with five Samoan tries proving Polynesian supremacy.
Welsh first five-eighths Neil Jenkins chose a bad day to overtake Michael Lynagh as test rugby's highest points scorer.
2007: Fiji beat Wales, 38-34
As World Cups have gone on, underdog fortunes have bloomed. Between the 2003 show and 2007, the tournament's average winning margin dropped by six points and the number of wins by less than 10 points went from seven to 16.
Argentina set the tone, by beating hosts France 17-12 on opening night and the French later passed the favour on (see below). But Fiji's deeds were the greatest.
Welsh fans maintain they fielded a weakened side against the Fijians, wanting to see how their fringe players would cope. The answer: not well.
Three tries in 10 minutes set the scene, winger Vilimoni Delasau scorching in for a 25-3 lead. The Welsh staggered back into it with three of their own, but the boot of Nicky Little left the islanders perfectly placed for prop Graham Dewes to crash over and decide the day.
2007: France beat the All Blacks, 20-18
Teams from Europe's Six Nations faced Southern Hemisphere opponents five times in 2007 pool matches. They lost all five. So when roly-poly England met Australia and the skittish French faced the All Blacks in Cardiff, a cheerful antipodean barbecue seemed on the cards.
It wasn't to be.
Australia, No 2 in the world rankings but - as always - the wobbliest of the Southern Hemisphere's big three, were ground down 12-10.
But the evening's later match blew the tournament wide open. The details are well documented: the forward pass, the questionable yellow card, the calls for Wayne Barnes' head on a stick. But we probably don't give enough credit to the French fire that night - they played at the edge of the rules and well beyond the limit of anything New Zealand thought they could manage.
"We played with a lot of heart," said French coach Bernard Laporte.
The All Black captain couldn't explain it.
"Mate, I'm not sure," said Richie McCaw. "I'm lost for words. If I knew the answers, we would have sorted it out."