South Australian captain Johan Botha claimed two key NSW wickets as the Sheffield Shield game in Adelaide hung in the balance at tea on Tuesday's second day.
In reply to SA's 288 all out, the Blues were 4-130 at the break, with Kurtis Patterson not out 31 and Peter Nevill on seven.
Redback skipper Botha (2-30) dismissed Scott Henry (15) and Ryan Carters, who made a well-compiled 65.
SA quicks Gary Putland (1-10) and Kane Richardson (1-15) were the other successful bowlers.
Earlier, SA batsman Callum Ferguson fell just short of a century when last man out in the Redbacks' innings.
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Ferguson, on 97, tried to pull a short ball from Steve O'Keefe but chopped onto his stumps to give the NSW spinner his fifth wicket.
O'Keefe finished with 5-89 from 36.2 overs while paceman Josh Hazlewood took 3-55 from 24 overs. Quicks Doug Bollinger and Trent Copeland claimed one wicket each.
