England locked out at Oval
England's bowlers had no answer as Graeme Smith marked his 100th Test with his 25th hundred and he and fellow centurion Hashim Amla wrested control at the Kia Oval.
Smith (131) and Amla (183no) batted through almost three sessions together to set a new highest second-wicket stand for South Africa against England.
Initially, they were sustaining the tourists' recovery. But by stumps on day three, after Jacques Kallis (82no) had also joined in, South Africa's 403 for two gave them massive power to add and put England, who posted 385 in their first innings, under extreme pressure for the remainder of this first Investec Test.
Smith and Amla reprised what they had witnessed themselves from Alastair Cook and Jonathan Trott two days ago. England's stone-wallers added a mere 170 in 58 overs after the loss of captain Andrew Strauss for a duck at the very start of this series.
After opener Alviro Petersen had also made nought on Friday, South Africa's captain and number three put on 259 together against a home attack rendered toothless on a slow pitch and able to take only Smith's wicket all day.
The slowest first 50 runs of Smith's 10-year career came from 160 balls, but he then stepped on the accelerator to reach three figures from only 41 more deliveries. By the time his chanceless innings was done, Tim Bresnan bowling him via inside edge and pad, he had been at the crease for more than six hours, kept out 272 balls and hit 20 fours.
Amla's nine-hour tour de force was often more pleasing on the eye. He reached his 15th hundred from 199 balls, having hit 13 fours, the pick of which were his seventh and eighth - memorable back-foot force past extra-cover off James Anderson and then a drive on the up in the same direction off Stuart Broad.
England surprisingly turned to Ravi Bopara, before Bresnan, and then switched Graeme Swann to the pavilion end - and there was even an over for Kevin Pietersen before the new ball was taken. But nothing Strauss did even hinted at a breakthrough, until Bresnan at last did the trick.
No respite was forthcoming thereafter either, Swann getting through 33 wicketless overs as Kallis underlined South Africa's domination in another century stand with Amla.
For the first time on home soil since Trent Bridge last year, Strauss' team will trail significantly after the first innings. Back then, Ian Bell's big hundred put them back in charge on the way to a landslide win over India. There is little time for that sort of outcome here, where the hosts will surely be grateful to grind out a draw.