The Scot recorded the joint second worst score of the day at the Gary Player Country Club in Sun City to fall four shots off the pace.
Martin Kaymer, one stroke behind Lawrie at the start of play yesterday, now holds a one-shot advantage at the top after a 70 that moved him on to a five-under total.
It was a good day for Germany with Kaymer's countryman Bernhard Langer winning the senior event by defeating American Jay Haas by two strokes.
Kaymer, the 2010 US PGA champion, said: "I am very happy for Bernhard that he could win this big tournament. It would obviously be nice to make it a double here but let's see what happens."
Second in the chase for the $1.25m first prize in the main competition is Louis Oosthuizen, who shot 69.
Fellow South African Charl Schwartzel (70) is a shot further back in third, with England's Lee Westwood (70) and American Bill Haas (71) tied in fourth place on two under.