Beijing: Allyson Felix justified her step-up to the 400 metres with a convincing world championships victory which helped send the misfiring United States team soaring up the medals table on Thursday.
Felix, the most decorated female athlete in history based around her 200m and relay expertise, clocked a blistering time of 49.26 seconds, the best in the world this year.
Shaunae Miller of the Bahamas claimed silver in a personal best of 49.67sec, with Jamaica`s Shericka Jackson taking bronze (49.99).
Felix, 29, has three world 200m titles to her name and is the reigning Olympic champion over the shorter distance, having previously bagged silver at the 2004 and 2008 Games.
But with several Olympic and world 4x400m relay golds on her resume, Felix wanted to test herself over the longer distance and it paid off spectacularly at a packed Bird`s Nest.
"It`s weird, it`s different to be down there for the 400m," the American said.
"I wanted to challenge myself this year and I did and I`m happy I could be successful and that I trusted in the plan and it came together."
Felix missed out on the Moscow worlds in 2013 because of injury after over-reaching two years previously in Daegu, where she attempted the 200-400m double but came away with just a bronze and a silver.
"It was a good time to step up to a challenge and see what I could do," she said of her decision to race just the 400m in the Chinese capital.
"I had to take advantage of the speed that I have and bring that to the 400m.
"I wanted to control the race," she said, acknowledging that she had tied up in the final 30 metres, with Miller and Jackson hard on her heels.
"I think everyone struggles at the end of a 400m!" she laughed.
Her world-leading time, Felix added, had given her "confidence in my fitness", one of her strong points according to coach Bobby Kersee.
"Bobby had been telling me all year long to really trust in it," she said. "It`s my first 400m title, it`s different but it`s a boost to get this one."
Felix acknowledged that her gold, coupled with Christian Taylor`s in the triple jump and Justin Gatlin`s 200m silver medal showing had been what the US team needed.
The performances sent the United States up to second in the table, three gold medals behind leaders Kenya.
"I think it was a great night. We`ve been struggling a little bit and it was a time to rally together. Hopefully we can keep that going," she said.
Felix, however, joked that she was not looking forward to Friday and watching the women`s 200m final.
"It`s weird, it`s bitter, it`s going to be hard to watch. But it`s going to be a fantastic race."