But Sanderson is also wary of a wounded Springboks side, who surrendered an 18-6 advantage on Saturday and fell apart when fly-half talisman Butch James went off injured.
James, flanker Pierre Spies and number eight Jacques Cronje are all out of the quickfire rematch next Saturday because of knee problems - with Gerrie Britz, Wikus van Heerden and South Africa sevens captain Kabamba Floors summoned as squad replacements.
England, though, have their own injury problems.
Sale Sharks pair Charlie Hodgson (knee) and Andrew Sheridan (ankle) both face further medical checks on Monday before head coach Andy Robinson's likely team announcement on Tuesday.
Neither player appears to have any realistic chance of recovering in time, but Robinson will probably make minimal changes following England's first Test victory since mid-February which was secured by second-half tries from wing Mark Cueto and replacement prop Phil Vickery.
"There is an amount of relief, and we all feel we have relieved a little bit of the tension and we can build on this performance," said Sanderson.
"We need to get a bit of momentum going, because there has been a bit of a rot to stop.
"There was no panic at 18-6 down. When you are playing at the very top level - and things are happening very quickly - it is important you keep a cool head. I thought we did that.
"But South Africa will come back even harder next week, and it is not good enough for us just to win once and be happy.
"We are about moving on and moving forward, and the true test is that we repeat the performance and get another win."
Robinson effectively gained a stay of execution after his team's 23-21 victory, although it was hardly an overall display to inspire job security.
Reviews and debriefs dominate the Rugby Football Union agenda to such an extent there can be no guarantee Robinson will survive much beyond next weekend.
But at least the world champions, who reach the third anniversary of that seismic English sporting achievement on Wednesday, made it eighth time lucky following a record-equalling seven straight losses.
Robinson said: "I am lucky enough to have had an involvement with England for the past six years.
"It has been tough - there is no doubt about that - but the commitment has never been stronger from the players and management.
"Everyone has pulled together; no one has looked at themselves, tried to split apart and thought they were bigger than the team. When I see that I know we can move forward.
"I would like to think this is a turning point for us. We've got a huge game next Saturday - and we have to build on this performance.
"If we don't perform next weekend all the hard work in the last 20 minutes of this game is wasted. I will remind the players of that all week - we've got to turn up next Saturday and really perform.
"It is about keeping the belief. There is no turning back in the way we play the game, but we've got to improve our execution and accuracy.
"I have tried to be totally honest with the players and the team management. If I ever felt they doubted me then it would put a lot of doubt in myself."