Dual-code great Scott Gibbs says Wales should beat South Africa for just the second time in their history when they clash in Sunday's World Cup pool game.
The former Wales and British and Irish Lions centre believes the Springboks are a side in decline.
"I think it's a great opportunity for Wales to upset the apple cart in the opening weekend," Gibbs told BBC Wales.
"There's more rhythm and momentum in the Welsh camp, and certainly more harmony."
South Africa are the defending champions and remain the bookies' favourites to top Pool D.
But Gibbs, who now lives in Cape Town, thinks there is plenty to suggest that Warren Gatland's side can add another win to the famous 1999 victory in Cardiff.
"I think South Africa as a rugby side have been regressing for the last 18 months and they're certainly not improving as a team," Gibbs said.
"I think there's a little bit of discord in the camp, there are certain players that are not performing.
"So if you look at that intelligence and the information it only leads to one thing really - I think it's a huge opportunity for Wales to get a valued scalp.
"On the basis that Wales have only beaten South Africa once in 100 years I think there's no better opportunity than Sunday to get that second vital win."
Despite Wales' current good form and fitness, Gibbs warns that it would be wrong to underestimate a still powerful South Africa.
"They are a confident nation and... notwithstanding they are in a low ebb of form and haven't had a great Tri-Nations, they're still very confident they can retain this World Cup," Gibbs added.
"I just don't buy into that confidence and when you look at the body-language of the players during the Tri-Nations and certainly last year's winter internationals, they don't look like a world championship side.
"They're a very proud nation and they're very physical and it's going to be a huge game for Wales, there's no doubt about that.
"If Wales win I think that will give them huge momentum going forward in the competition, but if South Africa lose I think there'll be a lot of finger-pointing and that may be the start of the end of the World Cup for them.
"They're under no illusions this is going to be their toughest game since the 2007 World Cup.
"Their recent win against New Zealand was much-maligned, the New Zealanders broke their line 15 times and probably squandered four or five chances where normally they would have taken them.
"South Africa haven't got a game at the moment: they can't create, the backline is very anaemic, they're so reliant on their front five to get them go-forward ball that I just don't see anything in their toolbox that can challenge Wales.
"But all that said and done, it's a World Cup and they're still third in the IRB [International Rugby Board] rankings and they are a side capable of upsetting Australia and New Zealand, England, France, Wales on their day.
"For me it's the game of the weekend and if Wales can ruffle some feathers against the Boks then I think it just sets them up beautifully for a very healthy competition."
After their Pool D opening encounter in Wellington, Wales and South Africa face games against Samoa, Fiji and Namibia, with the top two teams advancing to the quarter-finals.