Roberts and his Wales colleagues received a vibrant welcome from more than 200 people at Wellington International Airport and glorious sunshine enhanced the feelgood factor surrounding a Wales squad that has arrived in New Zealand on the back of five wins from their last seven starts.
Next Sunday's Pool D showdown will put the winners into a box-seat position in terms of potentially controlling an intense group that also features Samoa, Fiji and Namibia.
But lose against the Springboks - an experience Wales have only avoided on two previous occasions - and it effectively makes the following weekend's appointment with Samoa in Hamilton an eliminator.
"It's got all the ingredients to be a classic," said Wales and Lions centre Roberts.
"If you look at their players and the way they have played the last three or four years, you can see it hasn't changed much.
"They love to dominate the contact area, they play round the corner, they don't give the ball width and we know that's coming.
"That is why we played Argentina in the warm-up games. They are a direct side who base their game around a strong scrum.
"With South Africa, they are accurate in the air, they have a good kicking game and a guy like Morne Steyn, who can kick penalties from anywhere.
"It would be the perfect start to beat South Africa, but we are not looking too far beyond it.
"You can't underestimate any sides in our pool, and the boys know that you cannot focus on anything but our first match."
Wales will be captained for the first time in a World Cup game next weekend by their outstanding openside flanker Sam Warburton.
The 22-year-old has not only continued to produce world-class performances, but also relished a leadership role he first grasped against the Barbarians three months ago and then for a two-game August mini series with England while hooker Matthew Rees fought a losing battle to overcome neck trouble in time for the tournament.
But his aptitude has been no surprise to Roberts, a team-mate of Warburton's at regional and international level.
"Sam has done so well over the last couple of years, and in the last couple of months he has been brilliant, especially at the tackle area," added Roberts.
"He is an excellent role model on and off the pitch, and he has made that transition to being captain very easily."
Wales attack coach Rob Howley, meanwhile, believes he has a clear idea how Wales' meeting with South Africa will tactically unfold.
"They will go to the air a lot, playing a kicking game against us. It will be a ball-in-hand versus a ball-in-the-air game. That is what you will have," he said.
"The set-piece game, a firing lineout and ball in the air have been a strong part of South African rugby, and if you look at their record you can't argue with that.
"They are third in the world rankings, so they are doing a lot of things right.
"It's the power game, and you have got to have that. It's a given at the top end of the game.
"If you don't compete on the physical side, then you will come up short, and that is the number one part of the game against South Africa. You have to compete against them physically.
"I think there will be a lot of kicking in the World Cup. The ping-pong may come back into it as teams hunt territory, and it will be interesting to see how New Zealand and Australia go against the likes of France and Ireland in the pool stage.
"In our experience, when we play New Zealand, their kicking game doubles compared to other games. They kick a lot through Dan Carter, and they will change their kick-to-pass ratio depending on who they play."
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