The 22-year-old scored a hat-trick of tries and tallied 37 points, the most ever by a Springbok in a single Test.
The Boks thrashed Argentina 67–30 to move to the top of the Castle Lager Rugby Championship standings. Erasmus, who rarely singles out individuals, admitted this display was something truly special.
"Nobody can disagree. Sacha was brilliant on the day. You cannot become world-class overnight; it takes a lot of time, and we've thrown him in there consistently to ensure that he grows.
"I only think he has eleven international caps as well."
Captain Siya Kolisi echoed the praise, commending Feinberg-Mngomezulu’s composure and leadership on the field despite his young age.
Kolisi said while the flyhalf’s brilliance was clear to see, it was also the Springboks’ unity and belief that carried them to victory.
"I thought he was amazing, not just in the way he scored and created tries, but also how he controlled the game.
"But I think when we click as a team, every single player is able to show who they are within our system."
The emphatic win over Los Pumas lifted the Boks to the top of the Rugby Championship table with just one round remaining.
Kolisi said the team went into the clash with a “do-or-die” mentality, treating it like a semi-final, and stressed they approach every game as a must-win.
The Rugby Championship now heads for a thrilling conclusion, with the Springboks facing Argentina again in the final round, this time at Twickenham in London.
A win would secure Erasmus’ men the title ahead of rivals New Zealand and Australia. Kolisi added that the team will draw strength from the large South African expat community in the UK.