While there has been plenty of conjecture over the incident, World Rugby confirmed on Sunday that there had been no citings from the clash at Twickenham.
Ex-England halfback Matt Dawson said that if the shoe was on the other foot, England's players would be crying foul.
World Rugby has instructed officials to punish such offences severely in a bid to reduce the number of head injuries, but a lack of consistency is undermining the process. Ozzie referee Angus Gardner, in consultation with the TMO, Ireland's Olly Holmes, decided the hit was fair, and that secured victory by the narrowest of margins.
But Gardner, despite World Rugby's current crackdown on unsafe play, eventually decided against penalising Farrell's challenge, even though it appeared the England co-captain was leading with his shoulder. Farrell himself insisted there was no case to answer, however.
Former Ireland captain Brian O'Driscoll said the referee got the decision "spot on" while former Australia lock Justin Harrison said "just because you don't wrap doesn't mean it a shoulder charge, when laws of physics mean it's a bounce effect". He ran hard, it's hard to get your arms around when you're both hitting each other at that much force.
"I didn't feel lucky, my intent was to wrap my arm".
England, despite being a man down, were level when Farrell kicked a 45-metre penalty.
The Red Rose raised their game in the second half to gain revenge for a 2-1 series defeat in June, Elliot Daly scoring a magnificent long-range penalty and Farrell splitting the posts eight minutes from time after missing an earlier opportunity.
England were again grateful for another stray delivery from Marx, but it was only a matter of time before the visitors regained the lead and it was Nkosi who scored the opening try in the corner after more excellent work from the dominant Springboks forwards.
England sealed the narrowest of victories on Saturday courtesy of Owen Farrell's late penalty having turned around a 8-6 half-time deficit.
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