The former Lakeside High and University of Georgia standout's best throw of 69 feet, 93 inches came on his sixth and final attempt.
Christian Cantwell, of the U.S., won the title, beating Olympic champion Tomasz Majewski, of Poland.
Cantwell won with a throw of 72 feet, 3 inches, the best of the season, overtaking Majewski on the fifth of six attempts. Majewski took the silver with a throw of 71-103/4, while Ralf Bartels, of Germany, picked up the bronze with a throw of 70-11/2.
"I have won medals in the past but not that one. To win it in that fashion is even more exciting," Cantwell said. "I did what I wanted to do and it feels great."
Already leading after four throws, Majewski came up with his biggest toss of 71-103/4 on his fifth attempt. He figured it would be enough to add a world championship to the Olympic title he won in Beijing.
"I thought after that throw that it was over," Majewski said. "But Christian was very strong today. You could see it warming up, and he held up under the pressure."
The result was enough to give Cantwell, who has long been a dominant shot putter at smaller meets but one who has wilted under pressure in major events, his first world outdoor championship.
In other action, Usain Bolt cruised into the semifinals of the 100 meters.
Sprinting in earnest to test his groin, Tyson Gay did the same, setting up the prospect of a showdown in today's final.
Bolt, the three-time Olympic champion from Jamaica, and Gay, the three-time world champion from the U.S., proved they are in shape for the most anticipated race of the year.
Gay won his quarterfinal in 9.98 seconds, and Bolt cruised in at 10.03, finishing second in his heat.
After Asafa Powell flirted with elimination in the opening heat, he was all focus in the evening, clocking the fastest qualifying time of the quarterfinals with a run of 9.95, proving the pace of both the track at the Olympic Stadium and the quality of competition.
Just showing up, Bolt was the star of the day, bobbing and weaving his head, playing it up for the camera, and pointing to an adoring crowd. The most fun came during race.
He eased up at the halfway mark to see his training partner Daniel Bailey beside him and happily let him take the honor of winning in 10.02.
Gay had a slow start and needed to kick harder.
"My groin is pretty sore," he said.
Still, the American didn't think it would affect his speed today.
Powell redeemed himself after he eased up in his opening heat and only qualified by 0.02 seconds.
"I was running too easy. I underestimated the guys," Powell said. "It's kind of scary."
Dwain Chambers, of Britain, who tested positive for the steroid THG in 2003 and served a two-year doping suspension, won his quarterfinal heat in 10.04.
Just after the 100, the women's 10,000 was decided by fractions of seconds.
Linet Masai, of Kenya, broke Ethiopia's decade-long hold on the race with a blistering finishing kick that took a prematurely celebrating Meselech Melkamu by surprise. Masai finished in 30 minutes, 51.24 seconds to win by 0.10 seconds.