Marvellous Moeen takes the game away from persevering Proteas
Moeen Ali launched a destructive counter-attack to put England in firm control of the fourth Test and dash South Africa's hopes of staging a remarkable recovery.
The all-rounder - who starred with the ball to finish off the third Test with a hat-trick - crashed an unbeaten 67 from 59 balls including three sixes as England closed day three 360 ahead on 224-8 and, weather permitting, set for a 3-1 series success.
It was an end result many would have anticipated heading to Old Trafford on Sunday but, under mostly leaden Manchester skies, the Proteas made the most of the conditions to claw their way back into contention until Moeen's morale-sapping contribution.
Having conceded a first-innings deficit of 136, Morne Morkel (2-39) and Duanne Olivier (3-38) were particularly impressive in bringing South Africa back into the contest, England 289 ahead when the seventh wicket fell.
But Moeen - dropped at slip by Dean Elgar off Keshav Maharaj when just 15 - had other ideas, taking the attack to the tourists to the delight of an increasingly raucous crowd, who took particular pleasure in the left-hander thrice depositing his spin counterpart over the ropes.
Rain then brought an early end to proceedings which had begun in satisfactory fashion for England, who needed just 22 deliveries to claim the final wicket as Stuart Broad (3-46) ousted Olivier.
As the hosts looked to build on their commanding lead, Keaton Jennings was fortunate when put down on 0 by Elgar off Kagiso Rabada (2-37).
Morkel helped alleviate South Africa's disappointment by dismissing Alastair Cook for 10 in the next over, before also removing Tom Westley (9) courtesy of an edge to gully.
South Africa struck again after lunch as Jennings (18) played a lazy waft at Rabada and was held at slip, leaving his series average at 15.87 after eight innings.
Temba Bavuma put down a tough chance sprinting back from point to reprieve Dawid Malan, who failed to make the most of his second opportunity as he gave a bat-pad catch off Maharaj (1-92) to depart for six.
Joe Root was making seemingly serene progress towards a fifty but fell one short in playing on from Olivier, who picked up a second as Ben Stokes - having earlier survived a half-chance to Heino Kuhn at midwicket - nicked to slip for 23.
Olivier had his third after tea when Jonny Bairstow (10) pulled straight to Rabada at deep fine leg but South Africa were made to rue putting down Moeen.
Moeen went on the counter - going to fifty with his second six off the spinner, which he sent onto the England balcony where it was caught by a smiling Bairstow.
Rabada removed Toby Roland-Jones (11) and Moeen lofted Maharaj over midwicket for another maximum to further underline England's position of strength before the rain that had threatened since lunch finally arrived.