SIXTH-wicket pair Harry Nielsen and Cam Valente hold the key to a South Australian first innings lead after New South Wales turned the screws on day three of the Sheffield Shield clash in Adelaide.

Tom Cooper (40) was out the last ball before lunch, adjudged lbw to spinner Steve O’Keefe (1/31) after appearing to thick edge the ball onto his box. Cooper had put on 42 with keeper-batsman Nielsen in a promising union.

The Redbacks, 5-173, trail the Blues by 73 on the first innings.

Nielsen, covering for Australian Twenty20 vice-captain Alex Carey, made a pressure century (105) on debut for South Australia against Victoria February and will need to deliver again.

South Australia resumed at 2-113 but lost No.3 Callum Ferguson (36) and skipper Jake Lehmann (61) following an hour rain delay.

Ferguson copped a jaffa from debutant Daniel Sams (1/34) then former Test paceman Trent Copeland got his finger tips to a difficult chance at first slip.

Lehmann was rock solid before driving at Copeland (2/59) and edging to Nick Larkin at second slip.