Root cements England's control against troubled SA
England 303 and 172 for 3 (Root 60*, Taylor 24*) lead South Africa 214 (Elgar 118*, de Villiers 49, Broad 4-25, Moeen 4-69) by 261 runs
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Three days into this series England hold a 261-run lead over a South Africa side riddled with problems, chief of which was another injury to Dale Steyn after their batting had slumped in the morning session. Moeen Ali, who claimed 4 for 69, continued their difficulties against spin to earn a priceless 89-run advantage before England benefited from crucial fielding lapses to increase the lead steadily with Joe Root unbeaten on 60.
Any hopes that a return to home soil would ease the ills of the India tour for South Africa have not come to pass early in this series with England's impressive attack compounding the pressure on a fragile batting order. They lost 6 for 77 in the opening session as their first innings finished on 214 although Dean Elgar fought outstandingly to become the sixth South Africa batsman to carry his bat for 118.
Then Steyn pulled up after the second ball of his fourth over with a right shoulder injury and an attempted return was aborted after three deliveries. After play, though, the South Africa camp said the problem was being treated as "shoulder stiffness" after Steyn had been sent for a scan and there was hope he would be able to bowl on the fourth day although it may come too late to change the course of this match.
To further compound South Africa's woes their fielding also let them down. Dane Piedt had removed both openers - Alastair Cook lbw with one that slid on and Alex Hales defeated by drift to be caught at long-on - but in consecutive Morne Morkel overs shortly before tea they had the stuffing knocked out of them.
Nick Compton was shelled on 11 when Elgar missed a sitter at second slip and Root was missed on 6 when he gloved a pull which AB de Villiers, whose future was the subject of much speculation during the day, could not gather one-handed above his head.
Morkel put in sterling service in the absence of Steyn but, astonishingly, a third chance was to be missed off his bowling when Compton, on 45, edged a pearler only for de Villiers to grass another. That opportunity, at least, did not prove costly as two balls later Compton glanced Morkel down the leg side and de Villiers made amends. De Villiers puffed out his cheeks; Morkel just about managed a celebration.
By then, however, England's lead was over 200 on a surface offering considerable assistance for the spinners and a hint of uneven bounce. England's progress was never electric but time was on their side. Root made the most of his life with a 96-ball fifty which kept the scoreboard ticking over. He collected a six with a slog-sweep off Piedt and some of his off-side driving was a delight on a surface where few batsmen have found that sort of strokeplay easy.
At the start of the day there was not a consensus as to whether England had their noses in front or it was honours even. By the close there was no doubt after the match had been seized in the morning session.
As when Stuart Broad started the innings, it took him just two deliveries to locate the stumps, Temba Bavuma this time defeated by some low bounce outside off and dragging on an inside edge. There was certainly some variation in bounce, but it was also the shot of a batsman who had yet to get his feet moving early in the day.
In another shrewd piece of captaincy, Cook did not wait long to introduce Moeen with two left-handers now at the crease, one of whom, JP Duminy, who has had his travails against offspin. And it took Moeen just two balls to find Duminy's outside edge with a beautiful delivery which turned from middle and off, safely held by Ben Stokes at slip.
Kyle Abbott did not stay long, prodding forward at Moeen and getting a thick inside edge into his pad which was well held by James Taylor diving forward at short leg, although it needed the intervention of the third umpire after Rod Tucker had failed to spot the sizeable deflection.
The support provided by Steyn to Elgar suggested that he should be at No. 8 ahead of Abbott. Their stand took South Africa to the brink of the second new ball only for Steyn to try and send Moeen down the ground and instead find mid-off where Chris Woakes held the chance with a juggle. His spell ended on 12-3-24-3 and overall it was the first time Moeen had taken more than three wickets in an innings since facing India, at Old Trafford, in August 2014.
Steven Finn cleaned up the last two wickets in his first over with the second new ball to leave Elgar undefeated with his fourth Test hundred having brought up three figures from 211 deliveries. In an innings marked by his defensive technique, he continued to prosper on the leg side where two thirds of his runs came.
It was his second hundred in a Boxing Day Test, following the 121 he made against West Indies last year, and this was his first 50-plus score in ten innings. When the innings ended he became the first South Africa opener to carry his bat since Gary Kirsten against Pakistan in 1997. He may have to perform a repeat to save his team.
Andrew McGlashan is a deputy editor at ESPNcricinfo