"Every team would be pleased if Shane Williams is quiet," said Pieterson, who won his 22nd cap in Cardiff.
"It's always nice to play a Test match. It was physical, especially for the forwards. You could see that on the guys noses and faces!
"Our backs also had to get stuck in there. Test matches are never easy, but it was good fun."
Pietersen made his South African debut against Australia in 2006 after being plucked from obscurity by then Sharks coach Dick Muir. The 22-year-old has since scored 10 Test tries and was one of the most consistent performers during the Boks' triumphant 2007 World Cup campaign.
"Shane is one of the most dangerous players in the world of rugby so we did our job in keeping him quiet.
"He's one of the most experienced players in the world so it was a really tough task for me but I also want to thank the team for making it easier because everybody did their job."