GALLE, July 16 (Reuters) - Scoreboard at lunch on the first day of the first test between Sri Lanka and South Africa on Wednesday: South Africa won the toss and elected to bat South Africa first innings A. Petersen lbw b Perera 34 D. Elgar not out 62 F. du Plessis not out 14 Extras: (lb-1) 1 Total: (for one wicket, 29 overs) 111 Still to bat: H. Amla, AB de Villiers, Q. de Kock, JP Duminy, V. Philander, D.