Having lost flanker Tom Curry to a red card inside three minutes, England put on a masterclass of defensive organisation and forward control to win comfortably.
They were aided early on by the trio of drop-goals from Ford that moved them into a 12-3 lead and transferred the pressure onto the South American side.
"The crucial one was the third one, which took us more than seven points ahead," Ford told reporters. "In a tight game where it is hard to move the ball and score tries, to get more than seven ahead was big for us."
Ford said all the England flyhalves practice drop-goals at every training session in preparation for games like Saturday’s clash in Marseille.
"We have the nines (scrumhalves) pass us the ball and get the boys to put pressure on us to make it as realistic as possible," he said. "It is such a crucial weapon and we have seen before how influential they are at World Cups."
South Africa flyhalf Jannie de Beer kicked a tournament record five drop-goals to beat England in the quarter-finals in 1999 and Ford equalled the best previous mark for his team set by Jonny Wilkinson against France four years later.
"Five is a lot, isn’t it, but I thought I was on track at one point," he joked. "We were laughing in the change-room, out of this squad (scrumhalf) Danny Care was the guy with the most drop-goals for England. I thought I had to put an end to that."
Ford added that the warm conditions and World Cup ball are conducive to kicking.
"I think the temperature makes a massive difference. The ball is also different from the one we use in the Premiership. I am not sure what it is but it travels a lot faster in the air and a lot further."
Ford landed all his drop-goal attempts and kicked six from six off the tee for a perfect performance.
"That is the life of a kicker, some days you can’t hit a barn door, others everything goes over," he said.
