Australia's troubled Ashes tour hit an astonishing new low on Saturday as they descended to an unthinkable defeat against international minnows Bangladesh in their opening NatWest Series match.

On a day when Aussie internal strife and a sparkling maiden one-day international hundred from Bangladesh's previously misfiring Mohammad Ashraful conspired against the world champions, the result in Cardiff was one of the biggest sporting upsets of modern times - by five wickets and with four balls to spare.

Ashraful made exactly 100 at a run-a-ball to help defy universal expectations of a confidence-boosting success for out-of-sorts Australia - 100-1 on favourites at start-of-play - as he shared in a fourth-wicket stand of 130 in 23 overs with his captain Habibul Bashar.

The 20-year-old was caught at long-on off a low Jason Gillespie full toss immediately after reaching three figures, but that merely cleared the way for teenager Aftab Ahmed to send a partisan crowd into raptures with a six over deep midwicket to as good as seal victory when the same bowler tried a slower off-break with the first ball of the last over of the match - from which seven runs were needed.

Australia's perversely arrogant decision to bat first under heavy cloud cover combined with a traditionally slow Sophia Gardens surface to bring together two sides at opposite ends of the one-day international rankings - and as Bangladesh took advantage of massively improved batting conditions on a scorching afternoon there was no question which team felt the heat most severely.

On the back of two unexpected defeats to England and then Somerset in the past week, the Australians were compromised further by this morning's last-minute de-selection of key all-rounder Andrew Symonds for "breaking team rules" - an unspecified offence for which the Queenslander was scheduled to answer to an official investigation later tonight.

When early wickets also fell as Australia did battle with the initial elements and well-directed new-ball pace it quickly became clear the Ashes hopefuls were in for a much tougher test than anyone had anticipated.

They were indebted to a fourth-wicket stand of 108 in 26 overs between Damien Martyn (77) and Michael Clarke (54) - and an unbroken alliance of Simon Katich and Michael Hussey - as they were made to work hard for every run of their 249 for five by a disciplined Bangladeshi performance in the field.

If the underdogs stuck to their task commendably with the ball they were a revelation when their turn came to bat.

A sedate start was interrupted by the departure of Nafees Iqbal, who nicked one behind on the back foot off Gillespie - and there was to be a wicket each too for Brad Hogg and Michael Kasprowicz.

Hogg had number three Tushar Imran driving head high to be well held by Katich at mid-off, and opener Javed Omar cut Kasprowicz for another good catch by Matthew Hayden at backward-point.

That, though, was just the preamble to a scintillating stand between Ashraful and Habibul who came together at 72 for three and soon found themselves needing upwards of seven an over.

Ashraful responded with a display of wristy strokeplay which featured 11 boundaries in myriad directions as perplexed Aussie bowlers failed to contain his invention.

He had one serious escape, on 54 when Gillespie spilled him at long-leg off a hook at Kasprowicz. But he and Habibul made the opposition pay dearly - and by the time the captain was run out in a comical mix-up much of the hardest work had been done.

Ashraful's success was in stark contrast to the Australians' batting travails which were characterised by Martyn, who struck just one boundary - off the first delivery he faced - in his 80-ball half-century, while Clarke also had to settle for sensible accumulation on his way to a slightly slower 50.

The Australians were undermined at the top of the order by the well-directed pace of Mashrafe Mortaza and Tapash Baisya.

Opener Adam Gilchrist went for a duck to the second ball of the match, and captain Ricky Ponting managed just a single as his team stumbled to nine for two at one stage.

Gilchrist was out of the equation almost immediately when Mashrafe Mortaza rushed one through from a decent length to have the left-hander pinned lbw on the back foot, and Bangladesh were in business again when Ponting tried to make something out of nothing as he whipped across the line and was stone-cold in front to Baisya in the sixth over.

Hayden and Martyn were the men charged with righting the Australian ship - and they found Mortaza in miserly mood, conceding only five runs in his six-over new-ball spell.

Baisya's medium-pace looked the most vulnerable of the Bangladeshi options, yet it was he who ended up with three wickets - albeit for 69 runs in his 10 overs.

After Hayden had edged a loose drive back between bat and pad to be bowled by Nazmul Hossain, Habibul chose the early stages of Martyn and Clarke's stand to hurry slow left-armer Mohammad Rafique through his overs at the economical cost of only 31 runs.

As soon as they did try to up the ante there was immediate evidence that the caution had been well-placed when Martyn holed out at deep cover off Baisya and then Clarke was caught in the ring off the same bowler.

Katich and Hussey came to the rescue as 93 runs were added in the last 10 overs. In the end, though, it was not quite enough to stop Bangladesh recording only their 10th one-day international victory from 108 attempts - and adding Australia as the unlikeliest entry in their list of victims so far.