The 37-21 victory at Twickenham ended England’s 10-year winless streak against the Springboks, and earned coach Eddie Jones his 10th consecutive win.
“It is another step of building to where we want to get to, that is number one in the world,” Youngs said.
“South Africa are a huge rugby nation and beating them will give this team another layer of confidence.”
A dominant England ended their run of 11 defeats and a draw against South Africa, handing the visitors their fifth defeat in 11 tests.
Youngs outfoxed lock-turned-flanker Pieter-Steph du Toit twice to set up George Ford and Owen Farrell for successful tries.
The Leicester Tigers player, who debuted against Australia in 2010, has improved steadily under Jones and praised the Australian’s impact since taking charge.
“Eddie has been brilliant at instilling team belief and self-belief and today was an example of how much I am enjoying my rugby,” Youngs added.
England are looking to dislodge New Zealand from the top of the test rankings, but Youngs said the performance against South Africa also showed there was plenty of room for improvement.
“We need to control the ball better, have better discipline and want to put teams under more pressure,” he said.
“We allowed them to get good easy field position and not to have to work at times.
“We were able to come up with solutions pretty quickly, but on another day we might have had someone in the bin.”
New Zealand crushed Italy 68-10 in Rome on Saturday and play Ireland in Dublin next. England host Fiji on Nov. 19.
Original source: England ‘step closer to top’ after beating Boks