Bolt edged itpublished at 14:41
There was only 0.01 of a second between gold and silver, but that that's all that was needed for mightily popular victory.
Usain Bolt beats Justin Gatlin to win 100m gold
Bolt wins in 9.79 seconds; Gatlin 9.80 secs
Jessica Ennis-Hill wins heptathlon gold
Johnson-Thompson 28th after long jump failure
Aimee Lewis
There was only 0.01 of a second between gold and silver, but that that's all that was needed for mightily popular victory.
Michael Johnson
BBC Sport athletics expert & 400m world record holder
"Justin Gatlin fell apart a little bit at the end of the race. It was a stumble that wasn't caused by anything other than Usain Bolt. He got all off-balance and got ready too early for his lean. It was a Bolt-forced, un-forced error and he won't get this opportunity again."
Michael Johnson
BBC Sport athletics expert & 400m world record holder
"Usain Bolt was challenged here more than he has been at any time during his career. Put on top of that the burden of 'saving the sport' which was placed on his shoulders, it means that the pressure was there. I have to give him so much credit for that performance."
More from Usain Bolt: "This means a lot because I've been struggling all season, it's taken me a while to work things out. It's been up and down but it's okay now."
The organisers must head to the nearest shopping centre in search of an extra bronze medal because third place in the 100m will be shared between America's Trayvon Bromwell and Canada's Andre De Grasse.
Usain Bolt is asked by Phil Jones whether he understood why he was being regarded as the saviour of his sport and he says: "For me I understand why but I wanted to do it for myself also. It was a big deal."
Steve Cram
BBC athletics commentator
"Usain Bolt will walk away from tonight so proud of himself, and that's from someone who has so much to be proud of during his career. This may well have been his finest day."
Steve Cram suggests that this victory could be Bolt's "finest day". Gatlin was the bookies' favourite, the American was unbeaten in 28 races, he had set a world-leading time of 9.74 earlier this year but all that means nothing now.
Bolt draws level with Carl Lewis and Maurice Greene in the history books with three 100m world titles.
Mike Costello
BBC Radio 5 live athletics commentator
"I was astonished by Bolt's confidence after the Anniversary Games because he had struggled through the season but tiny margins change a season, and change the narrative. He hasn't wiped the slate clean but he's saved the sport from an awful lot of negativity."
Michael Johnson
BBC Sport athletics expert & 400m world record holder
"I'm amazed. This is Usain Bolt's best race ever. He knew it was a completely different set of circumstances for him. He'll be most proud of this win without a doubt. It's not about technique, it's about running for your life and he's got the talent to be able to do that."
Usain Bolt reveling in the crowd's adoration. Everyone wants to hug the Jamaican, everyone wants a picture of the greatest sprinter that's ever been. Gatlin being consoled on the sidelines.
Colin Jackson
Two-time world 110m hurdles champion
"It didn't take the best performance from Bolt to do the business, but he delivered when he needed to. He kept a cool head and worked it from gun to tape. Victory goes to the right person for me."
Colin Jackson
Two-time world 110m hurdles champion
"Justin Gatlin will kick himself because he will never, ever get a better chance to beat Usain Bolt."
It's easy to win Diamond League meetings, heats and semi-finals, so they say, but producing in a major final takes something else - and Usain Bolt has that something else. Gatlin tightened as he closed in on the finishing line.
The greatest that's ever been? Probably. The Jamaican now has nine world championship gold medals - three of them from the 100m.
Darren Campbell
Former British sprinter on BBC Radio 5 live
"We said there was always hope for Bolt and there was hope because Gatlin looked nervous. Gatlin's 9.77 in the semi-final would have been enough to win the final, but Gatlin couldn't open the lead he needed and he could feel Bolt coming and Bolt came.
"Talk about a hero - you've witnessed greatness!"
Steve Cram
BBC athletics commentator
"Bolt has saved his title, he's saved his reputation. He may have even saved his sport! It was the result that everyone wanted, apart from Justin Gatlin. How could we ever doubt him?"
Justin Gatlin must settle for silver. 9.80 seconds was his time as he seemed to stumble towards the end. Pressure perhaps?
He and Bolt were matching each other stride for stride until the Olympic champion powered through 10m out. "I've never been happier commentating on a 100m final," says Steve Cram.
What a champion. Usain Bolt started better than he has for some time... it was close, but the Jamaican successfully defends his title in 9.79 - his quickest time of the year. How could we ever doubt him, asks Steve Cram.
Hearts beating... the world watches on... Bolt the people's favourite...