Japan's diminutive Mizuki Noguchi put on an extraordinary display of front-running to win the Olympic women's marathon title on Sunday as Paula Radcliffe's challenge ended in bitter tears.

Noguchi, the world silver medallist who weighs just 40 kg and is 1.50 metres tall, produced a killer surge up a series of torturous inclines just after the halfway mark to break clear.

She hung on to win by 12 seconds, timing two hours 26 minutes 20 seconds.

Silver went to fast-finishing world champion Catherine Ndereba of Kenya in 2:26:32, with bronze for Deena Kastor of the United States in 2:27:20.

Noguchi managed a few words and then had to be carried out of the stadium after collapsing, overcome by the heat and humidity.

"I'm so glad," Noguchi said before her swift departure. "Thank you very much. A big thank you to the audience. It was very hot, very hard. I noticed Ndereba was coming closer and I thought she was going to catch me."

Noguchi's success followed Naoko Takahashi's win in Sydney. Japan have now won medals in the event at four successive Games.

Big pre-race favourite Radcliffe, who led for the first half of the race, failed to finish, breaking down in tears at the 36-km mark as she slipped back to fourth after two hours' running.

The Briton, world record holder and never beaten in three previous marathons, tried to re-start but then slumped down by the side of the road, sobbing. Her record was almost 11 minutes quicker than Sunday's winning time.

The event was staged between Marathon, the village which gave the event its name, and the Panathinaiko marble amphitheatre in the centre of Athens where the modern Olympic Games were revived in 1896.

Ethiopia's Elfenesh Alemu came fourth after being passed by Kastor late in the race.

The American did not even know she had won a medal.

"It was incredible. The whole last lap I was in tears. I didn't know if I had finished fourth or third."

Alemu's failure to win a medal was a double disappointment.

She is married to men's Olympic marathon champion Gezhagne Abera, who was denied a title defence in Athens by injury. He ran along the side of the course during Sunday's run, urging her on, before he was stopped by course officials.

The marathon had begun at 1800 local time but the heat was still intense. By five km, the lead group had already been whittled down to around a dozen.

Radcliffe, desperate for a first title at a major championships, was unable to fight her eagerness and broke to the front after 25 minutes, shadowed by the Kenyans, Ethiopians and Japanese.

Already the event, on a steadily rising course, was taking casualties. Lydia Simon of Romania, the Sydney silver medallist, was dropped and soon 10 were left at the front.

Kenya's Margaret Okayo, the fastest performer of the year, also lost touch as the race proper began.

After exactly one-and-a-half hours Noguchi made her move, blasting up yet another incline and exploding the leading pack of seven. Only Alemu was able to keep in touch but Noguchi kept attacking up the climbs to forge 15 seconds clear, then 30, with a third of the race to run.

Ndereba cut the gap to 12 seconds with two kilometres to go but Noguchi held on.