Sanchez scored a try, three conversions, a penalty and a drop goal to inch within 10 points of Felipe Contepomi’s record of 651 test points for the Pumas and lead his team to a rare success in the southern hemisphere competition.
Argentina outscored the Springboks by four tries to three in a fevered performance, aided by a litany of mistakes by their visitors.
Winger Bautista Delguy scored two tries in the space of four minutes while Ramiro Moyano went over for the fourth Argentine score. Substitute Lionel Mapoe scored twice for Boks and captain Siya Kolisi got their other.
It was only Argentina’s third win in 28 previous meetings with South Africa and came on the back of some powerful scrumming, fast breaks with skilful inter-passing and a resilient second-half defence when the visitors threatened a comeback.
The 29-year-old Sanchez increased his tally of career test points to 641 as he produced a sparking individual performance in the first half.
South Africa, who had beaten Argentina 34-21 in Durban last week at the start of this year’s Rugby Championship, scored the first try when Kolisi slipped a Sanchez tackle to burst through a porous defence.
And two quick scores from 21-year-old wing Delguy, in his first year of international rugby, and another from Sanchez had the Pumas firmly in control with a 20-point lead at half-time.
Delguy’s first, in the 19th minute, came after a line break by fullback Emiliano Boffelli. Then Delguy showed his pace and sidestepping skills in another quick break off the back of an advancing scrum for his second score.
Sanchez increased the home advantage after a quick dart down the left wing for a third home try and then produced a smart drop goal just before half-time to make it 27-7 at the break.
Second-half domination
Soon after the interval, Argentina made the task even harder for South Africa when winger Moyano scored to make it 32-7.
The Springboks dominated the contest after that and Mapoe went over twice, in the 48th and 65th minutes, but they failed to conjure up a comeback victory despite camping on the Argentine line, where they encountered stubborn defence and were forced into making crucial errors.
Argentina next meet world champions New Zealand in Nelson on September, 8 while South Africa play Australia in Brisbane the same day.
Earlier on Saturday, holders New Zealand beat Australia for a second successive week, this time 40-12 in Auckland.