On opening day, with all eyes on sprinters Asafa Powell and Tyson Gay and their predictable advancement in the 100, Dibaba emerged as the headline act.

She took the lead with a lap to go, kicked for home and beat Turkey's Elvan Abeylegesse for the gold medal with a time of 31 minutes, 55.41 seconds. Kara Goucher of the United States took the bronze.

After her tangle with Tufa, Dibaba said her stomach was stinging so much she had to hold her abdomen to dull the pain. Not only that _ she found herself behind by about 30 meters.

"I didn't think I could catch up," said Dibaba, who now try to add the 5,000 title for a second straight long-distance double.

The U.S. got off to a strong start in the nine-day competition, with Reese Hoffa and Adam Nelson finishing 1-2 in the shot put. Hoffa added the outdoor world title to his indoor gold. Defending champion Nelson won a medal for the fourth time in a row, adding to one gold and two silvers.

"When I finally won there was just this huge relief," said Hoffa, the season's top thrower.

Powell, the world record holder, breezed to victory in the second round of heats in the 100. He burst out of the blocks and eased up barely halfway through his second-round heat and still finished in the best time _ 10.01 seconds. He made sure he would not have to use one stride too many in the stifling heat at Nagai Stadium.

"It was as I expected, nothing else. All is going according to my plans," Powell said.

Even Gay admired the Jamaican.

"He looked pretty good," Gay said "It was kind of impressive."

In Gay's heat, another sprinter jumped the gun. Gay then struggled with his start on the second attempt and had to work to win in 10.06. Gay, with the fastest time in the world this year, has his eyes not only on the gold but Powell's record of 9.77. The semifinal and final are Sunday night.

"If I just execute my start I will be ready for tomorrow," he said.

Hoffa won the shot put with a throw of 72 feet, 3¾ inches, winning by 17 inches. Belorussian Andrei Mikhnevich, the 2003 champion, was third at 69-9½.

"To be very honest, Reese flat-out beat me," Nelson said.

In the first event of the program, Luke Kibet, a 24-year-old prison guard from Kenya, won the men's marathon by 79 seconds, the biggest margin in the history of the championships.

Kibet hit the tape in 2 hours, 15 minutes, 59 seconds. It was the slowest time at a major championship race at low altitude in 51 years, dating to the Melbourne Olympics. The marathon started at 7 a.m. and finished in 91-degree heat.

Mubarak Hassan Shami of Qatar was second in 2:17:18 and Viktor Roethlin of Switzerland took the bronze. The marathon is Japan's favorite event and the country's failure to win a medal was a huge disappointment to the thousands lining Osaka's downtown streets.

"I wanted to get a medal today, the color would not be important," said Tsuyoshi Ogato, who was fifth.

Carolina Kluft was in a good position to extend her five-year unbeaten streak in the heptathlon and win an unprecedented third straight gold in the event Sunday. The Swede got off to a great start, beating her personal best in the high jump and equaling her personal best in the 100 hurdles before surging ahead after three events.

Kluft totaled 3,121 points and held a big lead over Lyudmila Blonska of Ukraine, the season's top performer,who has 3,042. Britain's Kelly Sutherton has 2,950.