Graeme Smith and Neil McKenzie continued to frustrate England in the first Test at Lord's as South Africa got through their second session here on Sunday without losing a wicket.
The Proteas, following on, were 128 without loss at tea on the fourth day, still needing a further 218 runs to make England bat again but with both their openers having shown what was possible on a pitch still good for batting.
South Africa captain Smith was 71 not out and McKenzie 50 not out after four hours and 14 minutes of resistance, having defied all attempts so far by England captain Michael Vaughan to bemuse them with unusual field settings.
They resumed after lunch on 67 without loss. Left-hander Smith was then 36 not out with McKenzie unbeaten on 24.
Both men continued to bat in unhurried fashion and chose which balls to go after with care.
Smith's cut four off fast bowler Stuart Broad saw him complete a fifty off 106 balls - a fair run-rate for someone conscious of the need to preserve his wicket - with six fours.
As over after over passed without a wicket, the normally reserved Lord's crowd did their best to encourage England by roaring and clapping as the bowlers ran-in. They 'appealed' as well, but all to no avail.
McKenzie had a lucky break when he went to 48 with an edge off left-arm quick Ryan Sidebottom. But Vaughan had decided to do without a second slip and the ball went through the gap.
His single off left-arm spinner Monty Panesar saw McKenzie to a 190-ball fifty with seven fours.
The closest England had come to taking a wicket on Sunday was during the morning session when Smith, on 26, got a thin inside edge off Panesar.
But wicket-keeper Tim Ambrose had stood up too soon and the, admittedly difficult, chance bounced off his pads.
South Africa resumed on Sunday on 13 without loss, a huge 333 runs behind England's 593 for eight declared, built on Ian Bell's Test-best 199 and 152 from Kevin Pietersen in his first Test innings against the land of his birth.
The Proteas knew that if they batted as they did while being dismissed for a first innings 247, with Ashwell Prince's 101 the only major contribution, the opening match of this four-Test series could end with more than a day to spare.
Smith, whose decision to field first had backfired spectacularly, was eight not out and McKenzie one not out.
Panesar had taken four for 74 in the first innings but it was the quicks who'd made inroads at the top of the order.
However, there was a heartening moment for South Africa when, off Sunday's second ball, McKenzie cover-drove Sidebottom for four.
Smith, who in the corresponding match five years ago made 259, the highest individual score by an overseas batsman in a Lord's Test, then struck an elegant late cut four off Broad.
Panesar as happened on Saturday, got turn out of the footmarks outside the left-hander's off-stump. This proved a problem for Smith, troubled by the 26-year-old Northamptonshire bowler either side of his escape.
However, after lunch, Smith repeatedly moved way outside his off-stump to counter Panesar's spin and, in the process, decreased his chances of being given out lbw.