Mayank Agarwal hit his second century in successive matches on the opening day of the second Test against South Africa Thursday and said his side should aim for a 500-run first innings. The opener, who made a double century in India’s opening Test win, scored 108 after the hosts elected to bat. India were 273-3 when bad light forced an early end to play, with skipper Virat Kohli unbeaten on 63 and vice-captain Ajinkya Rahane on 18. Kohli and Rahane put on 75 runs for the fourth wicket to thwart South Africa’s determined bowlers who kept them under pressure as the gloom crept in. Agarwal, 28, said he was thrilled with his performance. “The team is in a good position, winning the toss, batting first and with one batsman short, it’s a good thing to make runs… 450-500 would be nice,” Agarwal said. “Try and get big runs in the first innings… (that) could help us in case we don’t want to bat again. It could really put pressure on the South Africans.” Kohli, leading the Test side for the 50th time, reached his half-century with a boundary off fast bowler Vernon Philander. But Agarwal took the lead role despite…