Radcliffe was targeting a time below 70 minutes in a head-to-head race with male distance running legend Haile Gebrselassie, who overcame a seven minute 52 second head start to win with ease.
The world marathon record holder, whose Team GB Olympic selection has already been confirmed, clocked one hour, 12 minutes and three seconds – her slowest ever half-marathon.
But she claimed a bout of bronchitis and pleurisy did not aid her preparations.
“I know that racing on antibiotics isn’t the best idea, and that is why I did not expect fireworks coming in,” she told BBC Radio.
“But I am at a loss to explain why it was quite so bad. I still would have expected and hoped for a time in the 69s.
“The thing that worries me is that I did not feel myself out there while running. The danger is that it affects my confidence. But I am not giving up on it by any means.”
Unlike Radcliffe, Gebrselassie has not had his Olympic place confirmed, which might explain why he was soon determined to do well, the two-time Olympic 10,000m champion overtaking pacemaker Philemon Rono after just 5km.
He eventually overhauled Radcliffe after 15.3km and then put down the hammer in the closing stages to clock one hour 52 seconds.
© Sportsbeat 2012
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BIOGRAPHY: Eric Bailly