Usain summons a Bolt from the blue

Usain Bolt once again produced his best when it mattered most to retain his 100 meters world title on Sunday and reassert his status as the fastest man on the planet.

The 29-year-old Jamaican surged past American Justin Gatlin over the last 30 meters and crossed the line in 9.79 seconds, his fastest run of the year.

Gatlin finished second in 9.80 to take silver, while Andre de Grasse of Canada and American Trayvon Bromell tied for third place in 9.92.

They will both be awarded bronze medals after they ran identical times down to a 1000th of a second.

Bolt, the reigning Olympic champion and world record holder, is now undefeated in the 100m or 200m in six major global championships going back to 2007.

"This definitely means a lot because I've been struggling all season," said Bolt, who has coped with injuries all season.

"It took me a while to figure out the problem and get it together, so I'm just happy."

He was disqualified from the shorter race at the Deagu world championships in 2011, and flirted with a similar mishap when he stumbled out of the blocks in the semifinals earlier on Sunday.

There were no mistakes when it came to final, though, and, back at the stadium where he first rocketed into the sporting stratosphere at the 2008 Beijing Olympics, he powered down lane 5 to edge Gatlin.

The 33-year-old American, a world and Olympic champion before the rise of Bolt and coming off a four-year doping ban, will perhaps regret dipping for the line so early - a move that disrupted his rhythm and reduced his speed.

The victory for Bolt will be an welcome boost for a sport that has spent three weeks locked in a public relations crisis after allegations of widespread doping among athletes.

"I understand why people thought it was important for me to win," Bolt added. "But as I said, I wanted to do it for myself. It was a big deal."

Bolt will go for successive sprint sweeps in Beijing with the 200 meters final scheduled for Thursday.