Springbok captain Victor Matfield paid tribute to his side's staunch defence as the world champions withstood a late rally from Wales to win 25-29 at the Millennium Stadium.
The victory kept South Africa's hopes of a Grand Slam alive after they brushed aside Ireland last weekend.
South Africa were 17-9 behind at the break but scored 17 unanswered points in the space of seven minutes to grab the initiative from Wales.
Wales refused to cave in and mounted a fierce late rally but couldn't breach the green wall.
"I'm very proud of the boys, they showed great character," said Matfield. "Wales put us under pressure and it was a great game for the spectators to watch.
"Well done to Wales, they really came out and played well. "(Defending) is something we really worked hard on (in training) and it came through and we were happy with that," he added.
Referring to a possible Grand Slam, Matfield said: "I don't know. There's still a fair way to go. We're focusing on Scotland and that's going to be another huge game. We will enjoy tonight and then start fresh from zero on Monday again."
GB7s women left their England base to train in Wales this week. Olympic Games hopeful Rachael Burford gives WRU TV's Graeme Gillespie her thoughts on Welsh teammate Jasmine Joyce - a 'one touch wonder'
The GB7s women's squad is currently training at Wales' Centre of Excellence where assistant coach Richie Pugh tells WRU TV's Graeme Gillespie some 'tough calls' will have to be made when it comes to finalising the 12 spots for Rio's Olympic Games.
Wales U20's Billy McBryde is looking forward to starting his first game against New Zealand this afternoon in the World Rugby U20 Championship where his side are looking to gain revenge from last week's pool defeat to the Kiwis.