Port Elizabeth, Opener Dean Elgar struck his third Test century as South Africa rode their luck to finish the first day of the second Test against West Indies on 270 for two on Friday.Elgar, who came into the match with his position under scrutiny, scored 121 as he shared a second-wicket partnership of 179 with Faf du Plessis which frustrated the touring side who were the architects of their own downfall as they let numerous chances slip in the field.Du Plessis will resume on a patient 99 along with Proteas captain Hashim Amla, who scored a double-century in the first Test in Pretoria and has reached 17.After being sent into bat, the day belonged to left-hander Elgar, who was involved in his fourth century stand in test cricket — remarkably all with Du Plessis. Following the early loss of out of form opener Alviro Petersen, caught at cover by Leon Johnson off Shannon Gabriel for 17, South Africa edged to 68 for one at lunch. They pulled away in the afternoon session though as sloppy West Indies offered four lives to the batsmen and were made to pay for their profligacy.Du Plessis had eight when he slashed the ball to Marlon Samuels at gully off Jerome Taylor, but was dropped.The right-hander, on 26, was also put down at first slip off left-arm spinner Sulieman Benn and the next ball the tall West Indian was left fuming as wicketkeeper Denesh Ramdin missed a stumping chance after Elgar skipped down the wicket with his score on 48. Elgar was fortunate to survive a run-out chance on 73 when he gave up halfway down the wicket having called an impossible single to mid-on.Brief Scores: SA: 260/2 (Elgar 121, du Plessis 99*) vs West Indies. — Reuters