Opener Stephen Cook made his second century in two Tests and South Africa built a hefty 432-run lead over Sri Lanka by the end of Day 3 of the first test on Wednesday.Cook was out for 117 but South Africa moved on to 351/5 in its second innings for a big advantage over the tourists after the teams tussled for superiority over the first two days. (SCORECARD)Cook’s century, his third in seven Tests since making his debut at the beginning of the year aged 33, came after his second century opening stand of the game with Dean Elgar (52).They put on 116 for the first wicket, and Cook then combined with Hashim Amla for a 105-run stand. Captain Faf du Plessis was 41 not out and Quinton de Kock undefeated on 42 in an unbroken 74-run partnership at stumps.Part-time spinner Dhananjaya de Silva took 2/74 for Sri Lanka but the tourists are on the back foot again in South Africa, where they have never won a series and only won one of 11 Tests over the last 18 years. They face a serious battle to get anything from this Test.Cook had to wait 15 years to be selected to play for South Africa. He then made a hundred on debut against England in January, and another century on tour in Australia last month.On Wednesday, he used his mechanical style – not attractive for some but proving to be effective – to wear down Sri Lanka’s bowlers on a pitch in Port Elizabeth that had been very helpful to the seamers on the first two days. Cook’s century came off 152 balls at a solid strike rate. He hit 11 fours in all and set up South Africa’s push for victory in the opening test of a three-match series.advertisementAlongside Cook’s personal milestone, it was only the 10th time that the same opening pair has made a century stand in both innings of a game.Cook went to an edge behind off Dushmantha Chameera and Sri Lanka’s frontline quick bowlers – Chameera, Suranga Lakmal and Nuwan Pradeep – had just one wicket each to go with two from De Silva.Lakmal, who took five in the first innings, had earlier removed Elgar, who tried to attack after passing 50 and lobbed a catch to midwicket. Amla was out lbw to Pradeep for 48, two runs short of what would have been a welcome first half-century in eight Test innings for South Africa’s leading batsman. Amla hasn’t reached 50 in Test cricket since August, and hasn’t made a century since January – now 11 innings.He stroked smooth drives for four to go with one slog over mid-on, but stepped across his stumps and was trapped on what turned out to be the last ball before tea. Amla’s dismissal was the 10,000th lbw in Test cricket history, a statistic that was flashed up on the big screen at St. George’s Park.Sri Lanka’s successes were sparse over the course of the day, though, with South Africa dominant from the start when seamer Vernon Philander removed De Silva for 43 off the first ball of the morning. Philander took two wickets in that opening over, finished with 5/45 for his 11th five-wicket haul in 38 tests. Sri Lanka was 205 all out in its first innings.