Durban (South Africa): England was set for a big victory in the first test after fast bowler Steven Finn's three key strikes late on Tuesday had South Africa 136-4 at stumps on the fourth day, still 280 runs short of an almost unreachable target.
After weathering a 53-run opening partnership, Ben Stokes broke through, and Finn then claimed the wickets of captain Hashim Amla, Dean Elgar, and Faf du Plessis to leave top-ranked South Africa tottering.
Finn's most important contribution was ending a stubborn 48-run stand between Du Plessis and AB de Villiers in the day's last over and five minutes before the close. That exposed South Africa's fragile middle order and put an early series lead firmly in sight for the English.
"We're in a fantastic position to try and press for that victory tomorrow," Finn said.
England's batsmen earlier ground down South Africa, with half-centuries by Joe Root and Jonny Bairstow helping set a formidable target of 416.
In the field, England found the opening stand between Stiaan van Zyl and Elgar only briefly troublesome, and Stokes struck with a quicker ball to bowl Van Zyl for 33. Finn's removal of Amla on 12 and opener Elgar for 40 in the space of two overs made sure South Africa had no chance of chasing down 416.
A draw also now appeared out of South Africa's reach after England bowled out South Africa for only 214 in 81.4 overs in the first innings. South Africa has batted 140 overs or more to save a test only once, in Australia in 2012.
England had removed the Proteas' top three batsmen in the last session and a half on Tuesday, and only De Villiers — on 37 not out — effectively stood between England and victory on Wednesday.
"He's one of the best players in the world so it's important to get him ... but we'll take any six wickets we can get," Finn said. "As long as we get those 10 wickets, it doesn't really matter how."
Finn ended Du Plessis' grinding 9 from 66 balls with a fizzing quick ball, the delivery of the day, which took the edge and flew to Alastair Cook at slip. Du Plessis and De Villiers resisted for nearly 24 overs, and that brought nightwatchman Dale Steyn out to survive the last three balls of the fourth day.
England has three full sessions to wrap it up on Wednesday.
"The batters coming in, we're really going to have to knuckle down and try and take it as long as possible," South Africa's Dane Piedt said.
In England's second innings earlier, the loss of batsmen Root and James Taylor for 42 fairly early in the day barely affected the push toward an early advantage in the four-match contest.
Root made 73 and Bairstow hit a rapid, attacking 79 from 76 balls to take England to a second-innings total of 326 all out soon after lunch. The tourists built partnerships all the way through their second innings: 73 between Root and Taylor, 71 between Root and Nick Compton, 48 between Bairstow and Moeen Ali, and 43 between Bairstow and Chris Woakes.
Root passed 50 for the 13th time in 26 innings in 2015, but missed the chance to convert that to a fourth century this year when he sent a top edge to slip off Kyle Abbott.
Taylor charged offspinner Piedt and was stumped.
Between their dismissals, Stokes fell for 5 trying a reverse sweep as England went on the attack.
Bairstow sent a big slog-sweep for six over square leg early in his knock to keep England forging ahead, and hit nine fours and three sixes in all. He was caught in the deep by JP Duminy off part-time bowler Van Zyl, who claimed three late wickets. Spinner Piedt took 5-153.
But by then England was already well ahead and expected to win. And while England applied the pressure with the bat, South Africa had to make do without injured fast bowler Steyn.
Steyn failed a pre-play fitness test in the morning after straining his shoulder on the third day on Monday. He couldn't bowl for the rest of this game and faced more tests on his right shoulder ahead of the second test in Cape Town, which follows quickly on Saturday.
England 1st innings: 303 all out in 100.1 overs (Nick Compton 85, James Taylor 70; Dale Steyn 4-70, Morne Morkel 4-76).
South Africa 1st innings: 214 all out in 81.4 overs (Dean Elgar 118 not out, AB de Villiers 49; Stuart Broad 4-25, Moeen Ali 4-69).
England 2nd innings: 326 all out in 102.1 overs (Jonny Bairstow 79, Joe Root 73, Nick Compton 49; Dane Piedt 5-153).
South Africa 2nd innings (target: 416): 136-4 after 47 overs (Dean Elgar 40, AB de Villiers 37 not out, Steven Finn 3-27).