England's seamers reduced Australia to 57 for four after 15 overs of the fourth NatWest Series match at the SWALEC Stadium.
Steven Finn and Boyd Rankin took a wicket each with the new ball as the tourists lurched to 11 for two, and then another two wickets fell for six runs in five balls to arrest the Australia recovery after a stand of 40 between Michael Clarke and opener Shaun Marsh.
England's hopes were therefore raised of levelling the series score at 1-1 here, with one more match to play in Southampton on Monday.
After Eoin Morgan won the toss, Finn and Rankin did not squander their opportunity to bowl on a pitch which spent much of the previous day and overnight under full cover with heavy rain falling.
In bright conditions and on a surprisingly pacy surface, Finn began with a tame wide but immediately made up for it with the day's first legitimate delivery - full, straight and swinging in just enough to beat Aaron Finch's attempted drive and send him back lbw for nought.
From the River Taff end, Rankin was on target from the outset and got his reward in his second over when Shane Watson's drive at a delivery which was not quite full enough resulted in an edge behind.
England's two frontline seamers kept the score to 31 for two in powerplay.
The first over of back-up medium-pace from Ben Stokes then cost 10 runs, but England's first-change repaid his captain's faith in his next.
Bowling with enough pace to beat Marsh's attempted pull, Stokes had his first international wicket - in his 13th limited-overs match - when wicketkeeper Jos Buttler held an athletic catch high above his head off the glove.
Finn returned to replace Rankin an over later and got rid of Clarke, who went to DRS after being hit high on the back foot by a delivery which nipped back.
Simulation depicted the ball just clipping the top of the leg bail and the Australia captain therefore had to go lbw.