Athletics: Sonia flops in seventh.
In her first big race in 18 months, the former champion could finish only seventh behind the flying Ethiopian Derartu Tulu in the World Cross Country long course championship.
It was a disappointing comeback for O'Sullivan who gave birth to her daughter Ciara last July.
Her lack of preparation showed as she struggled in the closing stages to finish some 37 seconds behind Tulu.
"I could have stayed at home and hid but I had to go through this," she said. "At least I know now where I'm at and what I have to do to get myself back in real racing condition for the Olympic Games.
"I was never in control of the race and never ever comfortable. They simply went too fast for me over the opening two laps and after that there was no way back."
Tulu, winning her third world title took on her Ethiopian team mate Gete Wami in a superb finish to win by just two metres at the end of the 8000 metre journey, in a time of 25 minutes 42 seconds.
Paula Radcliffe's dream of lifting her first ever World Championship title ended with her being stretchered off the course after collapsing at the finish.
Radcliffe found the scorching sunshine too hot to handle, as she slipped to fifth position during the final lap.