With speed to burn, Brianna Rollins unintentionally erred on the side of safety.
The former Clemson star and world record challenger got off to a sluggish start, avoiding a false start, with a 0.263 'reaction time' that ranked last in the field, but then streaked past reigning Olympic champion Sally Pearson of Australia to capture the IAAF World Championship in the 100-meter hurdles Saturday at Moscow.
Rollins, who set an American record of 12.26 seconds in the winning the USA Championship earlier this summer, finished in 12.44 seconds - a 0.06 margin over Pearson, who finished in 12.50.
Great Britain's Tiffany Porter was third with a career-best 12.55, and was followed by Americans Dawn Harper in 12.59 and Queen Harrison in 12.73.
Pearson jumped to an early lead and still held the edge after clearing the final hurdle, but Rollins, who was appearing in her first senior global final, had the speed in her legs to get upsides the 26-year-old Australian and dip to get the gold.
Rollins, turns 22 on Sunday, had signaled that she would be a title contender despite her youth, having run world's fastest time of the year earlier in the season, said she had understandably felt nervous as they settled into the blocks.
"My nerves got the better of me initially and I didn't get the best of starts but I calmed down quickly and set Sally as my target," she said. "It is alright to be nervous it is natural but it is how you react to that that makes the difference.
"To beat Sally in a world final is special as she is such a competitor and I am sure that my win will only serve to provoke her to want to regain her crown in 2015," she added.
For the season, Rollins - the NCAA champion - remained unbeaten at 25-0, including 17 straight collegiate races. She advanced to the final on Saturday by winning one of three semifinal heats in 12.54 seconds.