Aaron Finch wrestled control for Australia with a half-century to subdue England at Lord's.
The Australia captain extended his fine form to leave England on the ropes, sharing an opening-wicket stand of 123 with David Warner.
Warner fell to Moeen Ali for 53 as Australia reached 138 for one at the halfway point of their innings.
England won the toss and opted to bowl, but their failure to secure an early breakthrough could prove costly in this pivotal encounter.
Eoin Morgan's men can ill afford another defeat after losses to Pakistan and Sri Lanka, and clashes with India and New Zealand standing in the way of semi-final qualification.
Chris Woakes and Jofra Archer threatened early on but without reward.
And, in truth, England's opening pair needed to pitch the ball up and be more aggressive.
Skipper Finch appeared in fine form as he reached 74 not out at the halfway point, adding another milestone score to his 153 against Sri Lanka and three other half-centuries in the tournament.
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