World champion Sally Pearson loosened her vice-like grip on the rest of the field by slipping up in her final competition before the London Olympics.
The world's best 100m hurdler received a sharp reality check by being edged out by American Kellie Wells in cold, wet conditions at the Diamond League meet in south London.
It was only the Australian's second loss in nearly two years, her previous defeat coming when she crashed out after leading the Diamond League final in Brussels last September.
Pearson took a tumble warming up for the heats at Crystal Palace on Saturday and lacked her normal fluency on both her runs.
Her coach Sharon Hannan said the Queenslander suffered from back tightness following the fall but the injury was not serious enough to stop her competing in the final.
She entered the final as the red-hot favourite but Wells (12.57 seconds) managed to draw level at the seventh hurdle and finish over the top of Pearson (12.59s).
Hannan said the fall and the slippery track conditions could have played on her charge's mind after a gutted Pearson refused to talk to the media post-race.
"She is in seriously good shape," Hannan said.
"We have not seen any evidence that any other girls look like they are going to be able to run 12.2 in good conditions, that is the shape she is in right now.
"We are seriously confident in her preparation.
"I don't think that we have anything major to worry about."
In a statement passed on by an Athletics Australia spokesperson, Pearson said: "I was really disappointed. That was not good enough today."
Pearson is still a warm favourite to win the Olympic final on August 7 but Saturday's result was a reminder of the perils of predicting winners in the 100m hurdles.
"There are no guarantees in any event and certainly in hurdles, it is fraught with danger," Hannan said.
"Lots of things can go wrong in hurdles."
An ecstatic Wells celebrated her win by jumping around and pumping her fists in front of the Crystal Palace crowd that had pre-race handed Pearson one of the warmest receptions for a non-British athlete.
A stony-faced Pearson congratulated Wells and the result would have delighted the Australian's absent opponents such as Beijing Olympic champion Dawn Harper.
Wells said her victory proved Pearson was beatable.
"I think so," she said.
"I think anybody can beat anybody."
The American had her sights on the big prize next month - the Olympic gold medal.
"I don't go anywhere to lose," she said.