Australian Jana Pittman overcame another injury scare to advance to the final of the women's 400m hurdles at the Athens Olympics.

After running her heat, Pittman's troublesome left knee swelled up about 8.30pm, throwing a scare through the Australian camp.

But it proved to be nothing serious.

She finished second in her semifinal in 54.05 seconds behind world record holder Yuliya Pechonkina of Russia (53.31).

But the real surprise came in the second semi, where unheralded Greek Fani Halkia broke the Olympic record by clocking 52.77, almost half a second quicker than the Australian has ever run.

American hopes Sheena Johnson and Brenda Taylor also qualified for Wednesday's final with a minimum of fuss but countrywoman Lashinda Demus missed out.

Despite making the final Pittman said her knee, which was operated on two weeks ago, was still troubling her.

"Last night at about 8.30 it went boom," said Pittman.

"... it blew up quite badly, well not badly, but enough for us to ice-pack it for quite a while.

"But yet again I didn't feel it in my race so I'm really not worried about it."

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