Watch Ennis-Hill win heptathlon gold

Britain's Jessica Ennis-Hill produced a display of immense focus and fortitude to be crowned world heptathlon champion once again and complete a remarkable sporting return.

The 29-year-old Olympic champion only decided to compete in Beijing within the past month, having returned to training only last autumn after the birth of her son Reggie.

But she steadily built a near-unassailable lead over the first six events and then stormed through to win her 800m heat in two minutes 10.13 seconds to amass 6,669 points and leave Canada's Brianne Theisen-Eaton trailing 115 points down in silver.

Watch Ennis-Hill win heptathlon gold

Latvia's Laura Ikauniece-Admidina was 38 points further back in bronze.

The British one-two that had seemed a genuine possibility after the first day of competition disappeared when Katarina Johnson-Thompson dramatically fouled out of the long jump, the fifth event.

Johnson-Thompson slogged through the final two events under duress but was in tears at the end, her hopes of a first senior global medal dashed by a combination of inexperience and inaccuracy.

'I would have been happy with a bronze!'

Ennis-Hill was clearly stunned with her win and told BBC Sport that she would have been happy with third place.

"This is definitely one of the greatest moments of my career, I still can't believe it," she said. "Me and coach Toni (Minichiello) spoke about coming here, and we only wanted to come if I was able to compete for a medal.

"We spoke about the bronze medal and that it would be amazing for a silver medal, but we never spoke about gold. I kind of thought it was a little beyond me this year.

Ennis-Hill missed the 2013 Worlds through injury and was second in 2011 in Daegu

"There were doubts before the Anniversary Games but performing in London showed me I was making progress. If I'd come away with a bronze I'd have been so happy, so to win gold is unbelievable.

"This has been the hardest year ever. There were different pressures going into London 2012, but here juggling all my mummy duties has been even harder.

"I want to thank everyone for their help and sacrifices in helping me get back to being the athlete I was."

How Ennis-Hill won gold

Ennis-Hill, 29, began Sunday's second day by recording a season's best of 6.43m in the long jump, just nine centimetres off her personal best, and then threw 42.51m in the first round of the javelin to open up a gap of 86 points over Nadine Broersen of the Netherlands in the silver medal position and 94 over Theisen-Eaton in third.

Katarina Johnson-Thompson fails to register mark in long jump

That equated to a cushion of just under six seconds over the field in the 800m, and with Ennis-Hill boasting a personal best three and a half seconds faster than Broersen's and more than a second faster than that of Theisen-Eaton, the race was effectively a coronation.

Yet nothing about this win should be taken for granted, with a gold medal here arguably more impressive even than her Olympic triumph of 2012.

Where her rivals either underperformed or cracked under the pressure, Ennis-Hill was by contrast relentlessly consistent - a solid 12.91 seconds in the 100m hurdles, an equal season's best with 1.86m in the high jump, 13.73m in the shot put and 23.42secs in the 200m.

While several women have come back from childbirth to win distance-running titles, no multi-eventer has ever come back to win a world title.

And when her training was repeatedly interrupted by Achilles problems in the first half of this year, the Briton's hopes of even getting a qualifying score for these World Championships seemed remote.

Only an improved showing over the sprint hurdles at the Anniversary Games at the end of July persuaded her and coach Toni Minichiello that it was worth travelling to China, and then with a target of a podium place rather than a repeat of the world title she won in 2009.

After she had come past Theisen-Eaton in the home straight of the 800m, she fell to the track with her hands over her face. A road back that began with a 15-minute bike ride last November ended on a warm Beijing night in fairytale fashion.

'On her way to becoming a legend' - BBC pundits react

Michael Johnson: "This will be a great springboard towards Rio for Jess, and a fantastic confidence booster for her as an athlete. Already looking towards next year, it puts a lot of pressure on her rivals."

Kelly Sotherton: "I am really over the moon for Jess. That is one super woman. She is unbelievable - and on her way to becoming a legend.

"None of her performances here were outstanding but they were consistent and I see no reason why she can't do even better in Rio and defend her title."

Steve Cram: "What a performance from a true, true champion. If she wasn't already the darling of British athletics then goodness me, she is now. This is what it's all about - years of training to show that athletics can be pure and great and inspirational."

Harsh lesson for Johnson-Thompson

Her young compatriot and rival Johnson-Thompson had recorded no-jumps in the first two of her three long jump attempts but then appeared to have rescued matters with a huge leap in the third.

Yet after protracted and despairing discussions, the 22-year-old was ruled to have marginally fouled that one too and, with no points from the fifth discipline, her competition was effectively over - despite a later team appeal.

2015: Johnson-Thompson's day ends in tears

She had almost fouled out of another of her strongest events, the high jump, on the first morning, only clearing the relatively modest 1.80m on her third and final attempt.

Ennis-Hill, who tried to console Johnson-Thompson after the long jump, said: "It's awful. We're rivals and we want to better each other, but when she did that in the long jump my heart sunk for her.

"I felt really emotional for her because when you put yourself through two days of heptathlon it's really awful and it's hard work."

And although Johnson-Thompson came out for the javelin competition while the appeal continued, her demeanour told its own story.

After a fine first day - a personal best of 13.37secs in the 100m hurdles, another with 12.47m in the shot before an impressive 23.08secs in her first 200m of the season - she looked set to go head-to-head with Ennis-Hill in what was shaping up to be an epic 800m.

GB one-two in Rio?

To miss out on a world medal in such circumstances will be chastening, yet with the Rio Olympics a year away it is also a valuable lesson for a young athlete with a huge future.

The prospect of a showdown between the two Britons on the greatest stage of all is an alluring one.

But this weekend the spotlight is for Ennis-Hill only. She had pledged a performance to make Reggie proud, and just as in London three summers ago, she delivered in peerless style.