Australia's Jana Pittman was shocked at the new body shape of her Russian rival Yuliya Pechonkina after they both easily won their heats of the 400m hurdles at the world athletics championships today.

Pittman didn't get her wish to confront the world record holder in the semifinals at the Stade de France after she recorded the third fastest time while Pechonkina clocked the quickest.

World No.2 Pittman controlled her race throughout and eased off to clock 54.80 seconds, behind the muscular Pechonkina's 54.01 while American Sandra Glover won her heat in 54.48.

"She looked totally different to what I remember. Last year she was small and had long hair, now she's much bigger, she's a tank," Pittman said.

"But I've grown and changed as well.

"We ran similar races today, she looked quite comfortable but I expected her to run faster."

Pittman was drawn in the same semifinal as Glover and Britain's Olympic finalist Natasha Danvers while Pechonkina faces dual European champion Ionela Tirlea of Romania and South African Surita Febbraio who won her heat in 55.41.

Pittman, 20, went out comfortably from the start of her heat and led by 10 metres going into the home straight, with American Raasin McIntosh finishing second in 55.53.

"It was really easy, I was surprised how well I came off the eighth hurdle. Tomorrow, I'll run all the way to the 10th," she said.

"I'm pleased with the time considering I jogged the last 100 metres."

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