Athletics-Bolt digs in to advance to 100m semis

* Bolt safely through after unbalanced start

* Blames shaky blocks

* Semi-finals and final on Saturday

Usain Bolt took his first, somewhat stuttering, steps towards what he hopes will be a glorious World Championship farewell on Friday when he recovered from a poor start to win his heat in the first round of the 100 metres in 10.07 seconds.

The Jamaican is seeking his fourth gold in the event – he has won the 100m at every world championships since 2009 apart from 2011 in Daegu when he was disqualified for a false start.

It wasn't a false start on Friday, just a bad one, and Bolt said his blocks were to blame.

"That was very bad," he told reporters. "I stumbled a little bit coming out of my blocks. I'm not really a fan of these blocks. These are the worst blocks I have ever experienced. I have to get the start together as I can't keep doing this."

Asked what's wrong with the blocks, he said: "It's shaky. When I did my warm-up and pushed back, it fell back. It's just not what I'm used to. It's not as sturdy."

Bolt was given his usual rapturous welcome by the 55,000 crowd at the stadium where he completed the sprint double at the 2012 Olympics.

"The crowd is always wonderful," he said. "They always show me so much love and I always appreciate being here."

The fans were less pleased with America's world and Olympic champion Justin Gatlin, twice banned for doping offences and pipped by Bolt in the world championship final two years ago. He was loudly booed by many crowd when his name was announced and again when he won his heat in 10.05.

American 21-year-old Christian Coleman, the fastest man in the world this year with 9.92, looked smooth in winning the first heat in 10.01.

On a cool but windless night, Jamaican Julian Forte was the only man to break 10 seconds, clocking 9.99 for his first time under the magic mark.

The big surprise was South Africa’s Akani Simbine, who has been in hot form all season but finished fourth in his heat in 10.15 to scrape through as a fast loser.

The semi-finals and final take place on Saturday evening. Bolt is also due to go in the 4x100m relay a week later – his final championship race before retirement.