PERTH: South Africa increased their lead over Australia to an imposing 506 runs as they pondered a declaration at lunch on the fourth day of the first test at the WACA on Sunday. The tourists resumed on 390-6 on another hot morning in Perth and reached the break at 508 for seven, with Quinton de Kock (64) the only batsman dismissed. Vernon Philander was at the crease on 63 not out after reaching his fifth test half century with debutant spinner Keshav Maharaj alongside him unbeaten on 19. The highest successful fourth-innings run chase in test cricket was the 418-7 West Indies scored to beat Australia at Antigua in May 2003, while South Africa scored 414-4 to beat their hosts at the WACA in 2008. The Proteas will be confident of taking a 1-0 lead in the three-match series with five sessions remaining over the last two days of the test. They will have to take 10 Australian wickets without Dale Steyn, however, after their pace spearhead was ruled out of the series by a shoulder injury on Friday. After two days of dominance from South Africa, the hosts would have arrived at the ground aiming to remove the last few batsman as quickly as possible and get on with the run chase. De Kock was given out twice, once off quick Josh Hazlewood and once off spinner Nathan Lyon, but reviewed both immediately and was vindicated by the DRS technology. Philander survived a scare when it looked like he had holed out to fine leg off Mitchell Starc but Hazlewood spilled the ball onto the boundary rope to give up a six. Mitchell Marsh finally made the breakthrough when he got a little bit of bounce off the wicket and De Kock popped the ball up invitingly to Adam Voges at short leg half an hour before the break.