A few short months ago Katarina Johnson-Thompson made a startling confession: despite being one of the best athletes on the planet she suffered from impostor syndrome. Now even she must know that she is the real deal.

It was staggering enough to see her go toe-to-toe – and then topple – an all-time great in Nafi Thiam to claim a heptathlon gold medal in Doha. But it was the way she did it that really seared into both skin and soul.

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Over the two days of competition Johnson-Thompson never gave off a slightest whiff of weakness as she set four individual personal bests to keep Thiam at bay. And then, when victory was in the bag, she continued to push her body through the pain barrier on the final event, the 800m, to score 6,981 points – a tally that surpassed Jessica Ennis‑Hill’s British record of 6,955, which had stood as tall and imposing as an obelisk since London 2012.

As Johnson-Thompson burst into tears after crossing the line she said all the injuries, heartbreaks and self-eviscerations during the last few years were worth it. “It makes it more special and sweet for sure,” she said beaming. “This is crazy for me.”

Of course, this being Johnson-Thompson it was natural to fear some calamity or other would arise in the 800m, even when she had a 137‑point lead. A trip or a fall, perhaps, or even a random act of God. After all, at the Commonwealth Games last year she injured her calf with just 300m to go and had to do an impromptu triple jump – hop, skipping and jumping her way to victory. But this time there were no travails or torments, just another personal best of 2:07:26 and elation.

Facebook Twitter Pinterest Katerina Johnson-Thompson gives everything down the home straight in the 800m. Photograph: Lucy Nicholson/Reuters

Incredibly, she had beaten Thiam, who won silver, by 304 points – the biggest margin of victory in the heptathlon at the world championships since 1987 – with Austria’s Verena Preiner claiming bronze.

Johnson-Thompson had laid the groundwork on the opening day, setting personal bests in the 100m hurdles and shot put to lead Thiam by 96 points overnight. If the Briton was nervous going into the second day she disguised it like a master. She started with a massive long jump of 6.77m – her best in a heptathlon and well ahead of the Belgian’s 6.40m – to extend her lead to 216 points and never looked back.

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The question was whether Thiam could respond in the javelin. A heavily-strapped arm to protect an injured elbow suggested otherwise, and the Belgian could only throw out to 48.04m – more than 10 metres below her best. Johnson-Thompson’s response? Another personal best of 43.93m.

It meant Thiam had to finish nine seconds ahead of her in the 800m – and given that the Belgian’s personal best was eight seconds slower it was never going to happen. “I was always worried,” Johnson-Thompson joked afterwards. “I thought I was going to run out of the line in the 800m and I was going to get disqualified. I didn’t take anything for granted until I saw my name on the scoreboard.

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“Nafi is a phenomenal athlete, she has set the standard, she is one of the greats like Carolina Klüft. I witnessed 7,000 points first through her. She has raised the bar. I am glad I have been able to step up and be competitive.”

No wonder she was elated. It is a long time since she burst into the public’s consciousness at London 2012, an eager young apprentice learning at the feet of Ennis-Hill. Most expected a smooth succession, the flame passing from one Briton to another, but instead Johnson-Thompson had to suffer a seven-year itch before getting her due rewards.

Earlier in her career she would constantly visualise herself standing on the podium, the national anthem striking up and a gold medal round her neck, thinking that if she only believed enough it would happen.

Facebook Twitter Pinterest Katarina Johnson-Thompson threw a personal best in the javelin. Photograph: Kai Pfaffenbach/Reuters

If only. There were European and world indoor gold medals, and a Commonwealth Games triumph but when it really mattered injuries and ill-fortune got in the way. At the 2015 world championships she fouled three times in a row in the long jump while favourite. At the 2016 Rio Olympics a quadriceps injury flared up. Then, in front of her home crowd at the London 2017 world championships, she fluffed her lines in the high jump.

It did not help either that she was up against Thiam. But she accepted the challenge, and pushed herself to be even better.

“The low moments have helped me come back, to make the move to France, to take care of myself,” she said. “I am so happy with this.”

She also grew up. For years Johnson-Thompson was a self‑confessed “mummy’s girl” who had most things done for her. But moving to Montpellier in early 2017 to join a renowned group that included Kevin Mayer, the world decathlon record holder, changed everything.

“Moving to France has paid off,” Johnson-Thompson said. “It has been such a long road, I am glad I am coming into my best in these next two years.”

When she first arrived, her coaches would call her “droopy” because she used to drop her head in competitions, while her trainer, Bertrand Valcin, kept telling her to smile more. On a glorious night in Doha, she fulfilled those orders to the letter.