Ollie Pope's maiden Test century and another from Ben Stokes put England firmly in charge against South Africa on a dominant second day in Port Elizabeth.
The tourists declared on 499-9 and closed having reduced the Proteas to 60-2, a commanding position built around two brilliant knocks from men at different stages of their journeys.
Pope hit an unbeaten 135 in just his ninth Test innings while Stokes' 120 continued a remarkable sequence of performances that saw him crowned world player of the year this week.
The pair shared a stand of 203 for the fifth wicket, coming together on the previous evening at 148-4 and shaping the game together.
Weighed down by the exertions of 152 overs in the field, South Africa lost Pieter Malan and Zubayr Hamza to Dom Bess' off-spin in just over an hour's play before stumps.
Rain interruptions at both ends of the day saw eight overs lost and further bad weather now seems the likeliest reason to bet against England taking a 2-1 lead with one to play.
South Africa's prospects in the decider have already taken a considerable hit, with strike bowler Kagiso Rabada banned as a result of the overzealous send-off that followed his day-one dismissal of Joe Root.
