Hashim Amla hit the highest test score by a South African with an unbeaten 311 to put his side within sight of a crushing victory over England on the fourth day of the first test at the Oval on Sunday.
At the close England were 102 for four in their second innings, trailing by 150 runs.
Jacques Kallis stroked an unbeaten 182, his 43rd test century, as South Africa reached a commanding 637 for two before declaring at tea. Amla surpassed the previous record of 278 by team mate AB de Villiers.
"I'm happy, surprised and really excited that I have done something that's never been done before by a South African," Amla told reporters. "But the biggest pleasure is that we are in a really strong position to win this test match. That's my biggest joy."
The batsmen's marathon efforts were then supported by the bowlers as England lost Alastair Cook (0), Jonathan Trott (10), Kevin Pietersen (16) and Andrew Strauss (27) before the close.
Cook edged a probing ball on off stump from Vernon Philander to wicketkeeper de Villiers, Trott fell in similar fashion to Dale Steyn, while Pietersen was bowled by a straight delivery from Morne Morkel and Strauss top-edged a sweep to square leg off Imran Tahir.
South Africa, who will leapfrog England at the top of the world rankings if they win the three-match series, now have an excellent chance of taking a 1-0 lead going to Headingley for the second test on August 2. Their skipper Graeme Smith set the tone on Saturday with 131 in his 100th test match.
"When you've played quite a bit of test cricket you accept not every game is going to go for you and at the moment South Africa are in a dominant position," England batting coach Graham Gooch said. "That's stating the obvious.
"But the game's not over yet, you have to believe you can still get out of the game with a draw. If England do that, it will be a great performance."
Amla came to the crease on Friday at 1507 local time and was still there at 1540 two days later. He combined in a partnership of 377 with Kallis which was the highest-ever stand for the third wicket in a test in England.
England wilted in the bright sunshine as their bowlers toiled on a lifeless pitch that was still good to bat on and showed scant evidence of deterioration. They were unable to apply any pressure on the Proteas' batsmen for the third day running, after their innings began on Friday afternoon.
Amla went past his previous career best of 253 against India before lunch. The pace of his innings never changed as he continued to thwart England with a solid defence, attacking only when the ball merited an offensive stroke.
He became only the third overseas player to score a test triple century in England after Australians Donald Bradman, who twice achieved the feat, and Bobby Simpson. Amla reached the 300 with a lofted cover drive for four (his 33rd) off Tim Bresnan to go to 303.
It was the first test triple century in England for 22 years, since Graham Gooch hit 333 against India at Lord's in 1990.
Amla was embraced by Kallis and applauded warmly by the capacity crowd and his team mates on the players' balcony. Former England captain Michael Vaughan joked on Twitter that his signature beard had grown a centimetre since he came into bat.
Kallis was equally untroubled throughout his innings and he sought to raise the tempo only once he had passed his 150, striking off spinner Graeme Swann over mid-wicket for the first six of the innings.
Only India's Sachin Tendulkar (51) has scored more test centuries than the South African all-rounder.
Kallis celebrated his century before lunch by pointing to his eyes, a show of solidarity for wicketkeeper and best friend Mark Boucher, who was forced to retire from international cricket after suffering a serious eye injury before the series started.