The hosts were bowled out for 215 before the Aussies made 75-4 at the close of play.
Trott was two runs short of a half-century before he was skittled by Siddle, while the Aussie bowler claimed another victim in the form of Ian Bell (25) as the home side laboured to 178-5.
A disastrous second session continued to get worse when Matt Prior went for a single thanks to Siddle, who claimed his fifth wicket for the loss of 49 runs.
However, the home side started strongly with the ball as Shane Watson was dismissed by Finn for 13 before the paceman saw off Starc for a duck.
The prime wicket of captain Michael Clarke soon followed when he was bowled by Jimmy Anderson without having got off the mark.
That left the Aussies on 22-3 and they were another man down 31 runs later as Chris Rogers fell to Anderson.
Rogers was the last wicket to go for the day as Steven Smith (37 not out) and Philip Hughes (seven not out) ended at the crease.