Reigning holders West Indies inflicted a damaging defeat on Australia with an incredible six-wicket victory in Dhaka.
Australia set their opponents a target 179 to win in a game that neither side could really afford to lose in the race to reach the semi-finals.
Chris Gayle set the tone for the West Indies with a brilliant 53 from 35 deliveries, although they needed a superb partnership from Dwayne Bravo and captain Darren Sammy at the death to get over the finishing line.
Still requiring 12 from four in the final over, Sammy clubbed two sixes off the bowling of James Faulkner to clinch a remarkable success.
The result leaves Australia, fancied by many to go all the way in the one ICC tournament they are yet to win, in serious danger of failing to get out of the group.
Australia won the toss and batted first, scoring plenty of early boundaries but lost Aaron Finch, David Warner and Shane Watson in successive overs to end the powerplay on 41-3.
The in-form Glenn Maxwell provided the substance, hitting two maximums and five fours in his breezy 45, before Samuel Badree removed him in his final over.
Built the total
Brad Hodge built the total with 35 from 26 balls, while the slow-bowling trio of Badree, Marlon Samuels and Sunil Narine each claimed two wickets.
Gayle got off to a fierce start in West Indies' reply, flaying Mitchell Starc for four consecutive boundaries in the second over as he quickly warmed up, unlike his knocks against India and Bangladesh in previous matches.
Maximums off Doug Bollinger and Watson saw him race to 40 in just 14 balls, but his pace slowed comparatively as the score reached 87-1 at the halfway stage.
Rookie leg-spinner James Muirhead, brought in for veteran Brad Hogg, took the key wicket of Gayle, the left-handed opener holing out to Maxwell.
Lendl Simmons (26) and Bravo carried their side within sight of victory but it needed something special to achieve it.
Sammy duly provided it, taking the extremely expensive Starc for 19 in the penultimate over before his two decisive blows off Faulkner settled the contest and sparked wild scenes of celebration from the skipper and his squad.