At Friday's close Ashes-holders England were 52 for two in reply to Australia's first innings 527 for seven declared, a deficit of 475 runs, in a match the tourists, 2-0 down with three to play, had to win to stand any chance of regaining the urn. (Agencies)
England captain Alastair Cook, dropped on 15, was 36 not out and Jonathan Trott two not out after Clarke, whose innings was his highest against England, enterprisingly declared not long after tea.
Aggressive seamer Siddle was, surprisingly, the fifth of five Australia bowlers deployed by Clarke on Friday. But he responded by taking two wickets for two runs in 12 balls.
Siddle removed Joe Root, fresh from his 180 in England's crushing 347-run second Test win at Lord's, with the opener caught behind for a painstaking eight off 57 balls. He then had nightwatchman Tim Bresnan well held by wicketkeeper Brad Haddin.
Replays showed Bresnan hadn't made contact, the ball hitting his trousers, but, following consultation with Cook, there was no review.
Australia came into this match on the back of six straight Test defeats -- their worst run since 1984.
Star batsman Clarke, rather like Allan Border at the start of the Australia great's captaincy career in the mid-1980s, has often had to compensate for the weaknesses of his top-order colleagues.
Yet this was his 10th century in 27 Tests as captain, with his average as skipper of 65.15 well above his career mark of 52.52.
England's attack was led by Graeme Swann, the off-spinner's figures of five for 149 in 41 overs representing his 17th 'five-for' in 55 Tests.
But perhaps the most remarkable return of all belonged to England spearhead James Anderson, who finished with none for 116 in 33 overs on his Lancashire home ground.
At Friday's close Ashes-holders England were 52 for two in reply to Australia's first innings 527 for seven declared, a deficit of 475 runs, in a match the tourists, 2-0 down with three to play, had to win to stand any chance of regaining the urn.