Sanchez scored a try, three conversions, a penalty and a drop goal to come within 10 points of Felipe Contepomi's record of 651 test points for the Puma & # 39; s and lead his team to a rare success in the competition in the southern hemisphere.
Argentina beat the Springboks with four attempts to three in a feverish performance, aided by a litany of errors by their visitors.
Winger Bautista Delguy scored twice in four minutes while Ramiro Moyano took over the fourth Argentine score. Substitute Lionel Mapoe scored twice for Boks and captain Siya Kolisi got their other.
It was only the third victory of Argentina in 28 previous encounters with South Africa and came on the back of a few powerful scrumms, fast breaks with skillful interpassing and a resilient defense of the second half when the visitors threatened a comeback.
The 29-year-old Sanchez raised his score of career test points to 641 because he set a sparkling individual performance in the first half.
South Africa, which last week at the start of the Rugby Championship of Argentina 34-21 had beaten in Durban, scored the first time that Kolisi a Sanchez tackle to pass through a porous defense to jump.
And two quick scores from the 21-year-old Delguy wing, in his first year of international rugby, and another from Sanchez had the Puma's in control with a 20-point lead in half time.
Delguy & # 39; s first, in the 19th minute, came after a line-break by fullback Emiliano Boffelli. Then Delguy showed his tempo and sideways skills in another quick break from the back of an advancing scrum for his second score.
Sanchez increased the home advantage after a quick action along the left wing for a third attempt at home and then produced a smart goal just before the break to make it 27-7 during the break.
Soon after the interval, Argentina made it even more difficult for South Africa when Winger Moyano scored to make it 32-7.
The Springboks dominated the game afterwards and Mapoe passed twice, in the 48th and 65th minute, but they failed to win a comeback victory despite camping on the Argentine line, where they encountered stubborn defenses and were forced to make crucial mistakes.
Argentina then meets world champion New Zealand in Nelson on September 8, while South Africa plays Australia in Brisbane the same day.
Earlier on Saturday, the owner defeated New Zealand Australia for a second consecutive week, this time 40-12 in Auckland.
(Reporting by Mark Gleeson in Cape Town; Editing by Neville Dalton)