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Vernon Philander rocked England with a double strike late on the fourth day as South Africa cemented their grip on the third Test at Lord's.
The seamer removed both England openers during a superb spell of two wickets for one run in 10 balls.
At stumps England were 16 for two, needing a further 330 runs in a minimum of 90 overs on Monday's final day to reach what would be a new record victory total of 346.
Jonathan Trott is on six and Ian Bell on four after Vilander got two plumb lbw decisions - Alastair Cook for three and the captain Andrew Strauss for one.
The Proteas, 1-0 up in three-match series, will replace England as the world's number one Test side if they avoid defeat on Monday.
Hashim Amla, whose 121 was the cornerstone of South Africa's second innings 351, said England faced a tough task.
