If you thought you heard a rumbling noise coming from the Welsh valleys late on Saturday, it might just have been South Africa finally clearing their throat and announcing themselves at the World Cup. Okay, it could have been the Elton John concert taking place in Cardiff that same night, but South Africa, at the very least, are still standing in this competition.

Converting one win from five into a semi-final spot remains a task fraught with difficulty, not least because South Africa will likely have to beat the two teams currently sitting top of the table: Australia and New Zealand. It is Kane Williamson's unbeaten Black Caps up next, in Birmingham on Wednesday.

"Today we put our peg in the ground," captain Faf du Plessis said after Afghanistan had been brushed aside with a much-improved performance - although his team was rarely stretched by opponents low on confidence themselves. There were signs, certainly, of South Africa finding their spark with the ball, though Chris Morris, who claimed 3 for 13 from 6.1 straightjacketing overs, hinted that more improvement would be needed against New Zealand.

WATCH (India only): Highlights of Imran Tahir's spell against Afghanistan

"They are one of the favourites, to be honest," Morris said. "They have got a really good team. Well-balanced, well-led, and I don't want to call them dark horses because they deserve more than that. They are a really good, world-class team. Our disciplines are going to be have to even tighter against them because there's nowhere to hide from those guys. They are that good. They've got a seriously good bowling attack, a seriously good batting line-up. Destructive batting line-up. If they get going, they are difficult to stop. We are going to work quite hard in the next few days. We will have to be at our best to beat those guys.

"It's pretty simple. We have to win. There's no two ways about it. Faf is spot on in saying it's a quarter-final every time. We have to win. That possibly could bring out the best in us because we know there's nowhere to slip up. Slip up now and we are done."

We know we've lost, we haven't played our best cricket but the vibe has never changed. The vibe has been gun. It's a World Cup so what aren't you happy about
Chris Morris

The last time South Africa and New Zealand met at the World Cup, in 2015, we got one of the standout encounters of the competition, as Grant Elliott's penultimate-ball six left Dale Steyn, AB de Villiers and their team-mates bereft once again.

There is no Steyn or de Villiers this time - as anyone taking even passing notice of the first fortnight of South Africa's World Cup would know - but there is something to build on. Andile Phehlukwayo went as far as to say that they "mentally have the upper hand" over New Zealand, having beaten them in both of their bilateral series since 2015, though it seemed more the confidence of youth rather than an attempt to ramp up the pressure (since we all know how that has tended to turn out for South Africa).

"We've played against New Zealand a couple of times, and I think the last time we were there we won [and] against them at home, so I think mentally we already have that upper hand," he said. "Watching KG [Kagiso Rabada] running up and standing at mid-off and to see him bowling so well, and being unlucky at times - definitely, an unbelievable spell is coming from him. To see Bueran [Hendricks] bowl so well today was also unbelievable, coming in for Dale Steyn. Hopefully another clinical bowling performance like that comes about for us."

South Africa's attack could be further strengthened for the Edgbaston clash by the return of Lungi Ngidi, who has been working his way back to fitness after suffering a hamstring injury in their second match of the tournament. Rabada is also arguably yet to fire to his fullest, aside from a searing spell against India, which will likely mean trouble for someone at some stage.

Concerns around the batting haven't entirely been dispelled, with Hashim Amla looking far from fluent in eking out 41 from 83 balls in a low-intensity run chase again Afghanistan; following his concussion after being hit by Jofra Archer in the opening game, he will doubtless find his reflexes being tested again by the rapid Lockie Ferguson. But the Protea fire was warming up again by the time Phehlukwayo set an emphatic seal on victory by thumping six into River Taff (it went like a rocket, man).

"The vibe has never changed," Morris said. "We know we've lost, we haven't played our best cricket but the vibe has never changed. The vibe has been gun. It's a World Cup so what aren't you happy about."

Alan Gardner is a deputy editor at ESPNcricinfo. @alanroderick