Hashim Amla's unbeaten fifty steadied South Africa as England pressed with both bat and ball on the third day of the third Test at Lord's on Saturday.
At stumps, the Proteas were 145 for three in their second innings - a lead of 139 - with Amla 57 not out and nightwatchman Dale Steyn nought not out.
South Africa, 1-0 up in the three-match series, only have to avoid defeat to replace England as the world's top-ranked Test side.
Both teams had slumped to 54 for four in their first innings and South Africa were wobbling at 50 for two second time around before Amla, dropped on two, and Jacques Kallis (31) shared a third-wicket partnership of 81.
South Africa lost their first wicket when captain Graeme Smith, who'd made hundreds in his two previous Lord's Tests, missed a sweep against off-spinner Graeme Swann and was lbw for 23.
Amla was fortunate when he glanced Stuart Broad down the legside and diving wicket-keeper Matt Prior just failed to cling on to the left-handed chance.
But two balls later, Broad had opener Alviro Petersen, playing across the line of a full delivery, lbw for 24.
Both Amla and Kallis initially struggled against the short ball before Kallis lofted Broad over gully for four.
Amla too found his touch, cutting Swann, who bowled 20 overs unchanged for a return of one for 38, and easing James Anderson off the backfoot.
But a few overs before stumps, Kallis was lbw to fast bowler Steven Finn, with Australian umpire Simon Taufel's decision upheld on review - much to the batsman's obvious disappointment.
Amla, however, drove Broad down the ground to complete a 95-ball fifty with his seventh four and, two balls later, elegantly stroked him through extra-