First Broad made a fluent 32 as he shared an eighth wicket stand of 58 with Matt Prior (30) that ensured Australia would have to bat again in a match the tourists had to win to stand any chance of regaining the Ashes.
The pair then combined to remove Australia opener Chris Rogers for just 12 when fast-medium bowler Broad took the left-hander's outside edge and wicketkeeper Prior, diving in front of first slip, held a good catch.
David Warner a noted one-day opener sent in at the top of the innings instead of all-rounder Shane Watson in a bid to score quick runs after missing the first two Tests of this series after being banned for his bar-room attack on England's Joe Root in June, was 12 not out. Usman Khawaja was nought not out.
Australia captain Michael Clarke, who made 187 in his side's first innings 527 for seven declared, faced a tricky dilemma.
But he also knew too early a declaration could give England a chance of victory in a match so far largely dominated by Australia.