Usain Bolt ran his first race at this year's world championships in Moscow on Saturday, and easily qualified for Sunday's semifinals.

The two-time Olympic champion in the event is trying to regain the world title he surrendered two years ago in South Korea, when he false-started in the final and was disqualified.

He still went on to defend his title in the 200 and the 4x100 relay.

Bolt won his heat Saturday in 10.07 seconds, leading the entire way and cruising across the line.

Toronto sprinters Aaron Brown (10.15) and Gavin Smellie (10.30) qualified for the 100-metre semifinal by finishing in the top three in their respective heats.

Calgary's Sam Effah (10.21) finished fifth in his heat and just missed qualifying. The three best times outside the top three in the heats qualified for the semifinal, and Effah's time was fourth.

The race started with a false start, but it wasn't Bolt this time. Instead, it was the runner to his right, Kemar Hyman of the Cayman Islands.

"I wasn't really worried," Bolt said of the false start. "I was a listening for the gun, so that was good."

It did not phase him one bit. After all, the stadium had been filled with the reggae sounds of Bob Marley's classic "Three Little Birds," with the lyrics "Don't worry, 'bout a thing. 'Cause every little thing is gonna be all right."

Casual as ever, Bolt made his outing seem like a breeze.

"I didn't try to run too fast," Bolt said. "I was trying to work on my technique to get it right. Tomorrow, I will put more speed into it."

Bolt also won the 100, 200 and 4x100 relay at the last two Olympics, though he hasn't set an individual world record since the 2009 worlds in Berlin.

Freak accident

Discus thrower Natalia Semenova of Ukraine was injured in qualifying Saturday in a freak accident.

Semenova was sitting on the bench in the infield when Zaneta Glanc of Poland spread her arms and imitated a throwing motion while holding the disc in her hand and hit Semenova on the nose.

Semenova's coach said the athlete's nose may have been broken but there was no immediate word from the Ukrainian team on the severity of the injury. She made one throw of 55.79 metres but failed to reach Sunday's final.

Farrah golden

Now Mo Farah has a world championship gold medal in the 10,000 to go with his Olympic title.

In a tantalizing finish, Farah had to fight off defending champion Ibrahim Jeilan over the last 150 metres. But instead of giving in at the line like he did two years ago, his finishing speed was such that he had time to cover his face with his hands and cross the line with his arms wide open.

Farah, who ran the race in 27 minutes, 21 seconds now has to defend his 5,000 title next Friday and, at 30, establish himself as the defining long-distance racer of his time with another long-distance double.

"I won the medal that was missing," Farah said.

The top Canadian was Mohammed Ahmed, who finished ninth (27:39:76), while Cam Levins was 14th (27:47:89).

Farah had been honing his finishing kick all season, and when he became the fastest European o14th (f all time over 1,500 metres last month, he knew he was a world beater.

So did all of Britain, convinced he could do as well as his double at the London Olympics, and the relief of living up to expectations was visible as soon as he crossed the line.

The relief was all the more so since he almost tripped when he briefly surged into the lead with about four laps to go.

He kissed the Mondo blue track and fell on his back looking up at a sky over the Luzhniki Stadium which was just as perfectly blue.

Temperatures were close to 27 degrees when Farah ran.

'He's on fire'

Gunnar Nixon already set the decathlon ablaze as the 20-year-old American competing in his first major global event took a big lead over Olympic champion Ashton Eaton after four of 10 events.

The world junior champion made his big move by clearing 2.14 metres in the high jump while Eaton failed to go higher than 1.93.

"So far, he's on fire. I hope he keeps it up," said defending champion Trey Hardee, who failed to clear any height when cramps affected his jumping and later pulled out.

Nixon has 3,611 points overall, with Michael Schrader of Germany in second with 3,501 and Eaton is third with 3,495.

Kiplagat repeats

Defending champion Edna Kiplagat of Kenya won her second world championship title in the women's marathon, making a late surge to pull past Valeria Straneo of Italy.

Kiplagat won in 2 hours, 25 minutes, 44 seconds.

Straneo had led from the early minutes of the race on a flat course along the Moscow River. But Kiplagat made her move at the 40th-kilometre mark and finished nearly 15 seconds ahead of Straneo.

Kayoko Fukushi of Japan won bronze.

Canada's Lanni Marchant was 44th, with a time of 3:01:54, a season best.

With files from