England's pace attack piled the pressure on South Africa and eventually got minor reward, on the fourth morning of the third Investec Test at Lord's.
In a match England must win to share the series and stop the tourists taking away their world number one status, Hashim Amla (75no) and nightwatchman Dale Steyn kept the hosts at bay for 45 minutes.
Steven Finn and James Anderson provided a stern test for both batsmen - but it was not until Graeme Swann was introduced at the nursery end, and Stuart Broad came on for Finn - and got Steyn in his first over - that England made the breakthrough as South Africa reached 183 for four, and a lead of 177, an hour before lunch.
South Africa's first run of another glorious morning had been a painful experience for Steyn, hit on the left glove by a bouncer from Finn and needing treatment after scampering the single.
The tailender was also responsible for his team's first boundary, after almost half-an-hour, when he clipped Anderson off a thick inside edge past midwicket to bring up the 150.
Broad, however, made short work of Steyn - who succumbed to yet another short ball, trying to fend off again but offering a simple catch off the shoulder of the bat to short-leg.
Amla's new partner AB de Villiers announced himself with successive boundaries from his first two balls, pulled fine off Broad and then down the wicket to hit Swann over mid-on.
Such was the nature of a finely-balanced contest, England needing to restrict their chase on Monday to stay in contention, they could afford little more from either De Villiers or Amla - with several often productive South Africa batsmen still to come.
It looked a hammer blow therefore when Anderson continued his uncharacteristic recent trend of missing catches, this time a straightforward one low at midwicket to reprieve De Villiers on eight after Swann had deceived him in the air.