Australia's Ashes tour fell another peg as it suffered an embarrassing loss to county side Somerset - the world champions' second slap in the face in three days.

The Aussies piled on 5-342 and had Matthew Hayden (76) and Ricky Ponting (80) retire but were stunned as Somerset reached 6-345 with 19 balls to spare.

South African captain Graeme Smith smashed 108 from 74 balls and Sri Lankan hitter Sanath Jayasuriya struck 101 (79 balls) in an astonishing opening stand of 197 which set their side up for a memorable victory.

Australia's loss came just two days after it was rolled for 79 and beaten by England by 100 runs in the Twenty20 match in Southampton.

In further bad news, paceman Brett Lee left the ground with shoulder pain in his right bowling arm, while batsman Damien Martyn was off the ground for most of the second innings with hamstring tightness.

Lee will undergo scans in Cardiff over the next couple of days to determine the extent of the problem, which ended his day after bowling just four overs for 0-26.

With him off the ground and Michael Kasprowicz (0-89) and Shane Watson (1-72) belted mercilessly, Australia was powerless to stop Smith and Jayasuriya, who hammered 26 fours and four sixes between them.

Even with Somerset teetering at 6-291, Australia could not hold out as locals James Hildreth (38 not out) and Carl Gazzard (21 not out) steered their side home.

Even though the ball was wet - the game went on despite showers - Australia had a disastrous day in the field and would have conceded 30 runs through misfields and fumbles.

The only thing that would have pleased Ponting would have been the form of the batsmen, as he and Hayden both walked off to give their teammates some decent time in the middle.

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