Usain Bolt had the weight of the world on his shoulders at the 2015 IAAF World Championships.

The Olympic legend had practically been indomitable from the moment he first set the 100-metre world record in 2008, but there was a major threat for him to contend with seven years later in Beijing.

Just as Yohan Blake had made a surge ahead of the 2012 Olympics, even defeating Bolt in both the 100 and 200 metres at the Jamaican trials, none other than Justin Gatlin was making a charge of his own in 2015.

Bolt vs Gatlin in 2015

Something of a pantomime villain in athletics due to twice serving a doping ban, the American was in the form of his life ahead of the World Championships in China having opened up his season with a personal best.

The scintillating time of 9.74 seconds that Gatlin - one of few sprinters to ever beat a prime Bolt over 100 metres - posted at a Diamond League meet in Doha really set the stage for a titanic battle at the competition that mattered most.

And when the championships eventually got underway at the iconic Bird's Nest stadium, there were worrying indications of the form that Bolt found himself in ahead of an inevitable showdown with Gatlin in the final.

Bolt's tough journey to the final

That's because the legendary Jamaican didn't enjoy the smooth-sailing journey through the heats and semi-finals that track and field fans had been used to seeing from him.

Whereas in the past Bolt had cruised through the qualifying rounds, slowing down metres upon metres before the line, he really had to put his foot down in order to even reach the final in 2015.

And that's what brings us to Bolt's semi-final race that year because it endures as one of the most unique and impressive of his career performances all these years later, producing a truly incredible comeback.

While it's been painfully exaggerated by casual fans over the years that Bolt is some kind of awful starter, there could be no denying that he experienced a shocking start out of the blocks on this occasion.

Bolt sprinting at Beijing 2015.

Usain Bolt of Jamaica starts in his men's 200 metres heat at the 15th IAAF World Championships at the National Stadium in Beijing, China August 25, 2015. REUTERS/Phil Noble

In fact, just 10 metres into the race, you'd be forgiven for thinking that Bolt was genuinely going to fall over as he leaned incredibly far forward in a clear loss of balance.

And although he eventually regained his form and posture, the impact was damning with the reigning world champion finding himself as far back as third-last with the halfway point of the race approaching.

An epic 100m comeback

However, when you're talking about the fastest human being in recorded history, you have an ability to find an extra gear that literally nobody else has - and that's exactly what the great man reached for.

So, be sure to bask in Bolt's greatness by checking out his frankly remarkable display of escapology, eventually managing to win the heat by a split-second, with a full race replay down below:

Absolutely unbelievable. From disaster to delight in no time at all.

Despite us having been so used to see Bolt strolling through his heats year in, year out, this was an almost entirely unique scenario where he had to dig deep and slam the accelerator pedal in order to make up for his mistake.

A win for the ages in the final

However, although Bolt still managed to pull the rabbit out of the hat, you can understand why the performance was nevertheless concerning as he prepared for his long-awaited clash with Gatlin in the final.

But as is so often the case with all-time greats, Bolt delivered when it mattered most, putting together an excellent race to ensure that he was ready to pounce when Gatlin lost his form in the dying metres of the race.

Bolt duly nipped across the line by a nose-hair to regain his world title and although it was by no means his fastest ever performance, it might just be his most impressive gold medal given the circumstances.

And that simply wouldn't have been possible without his Herculean comeback in the semi-finals.