South Africa continued to pile on the runs against Bangladesh in the first test on Friday (29), reaching 411-1 at lunch on the second day with a 215-run partnership between Dean Elgar and Hashim Amla.
Elgar moved to 172 not out and Amla was 137 not out for his 27th Test century.
The pair put on 113 runs in the day's first session at a run rate of over four an over, and South Africa was already looking at the timing of its declaration.
Bangladesh's bowlers still had no success on a placid Potchefstroom pitch, underlining the tourists' error when they chose to bowl first after winning the toss.
South Africa took advantage in a big way after being given first use of the pitch. Elgar and Aiden Markram (97) put on 196 for the first wicket on day one and Elgar and Amla continued the Proteas' dominance.
The only wicket to fall was a run out when Markram and Elgar got into a mix-up on the first day and Markram missed out on a century on his test debut.
On Friday, Elgar went past his career-best score of 140 and Amla's century took him level with Graeme Smith for the second most hundreds in test cricket for South Africa.
Jacques Kallis is still some way ahead with 45 centuries.
South Africa and Bangladesh will play two tests, with the series Ottis Gibson's first in charge of South Africa.
