Australia captain Michael Clarke believes his century and the efforts put by other batsmen to put a huge first innings score against England won't matter in his side fails to win.

Peter Siddle took two wickets shortly before stumps on the second day of the third Ashes Test at Old Trafford to cement a strong Australia position built by captain Michael Clarke's 187.

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.

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, AFP report.