Asher-Smith, who won silver in the 100m on Monday, came off the bend in the lead and extended her advantage down the home straight to cross the line in a British record of 21.88sec.
The 23-year-old British sprinter had been the favourite coming into the race after her most high-profile rivals dropped out through injury, fatigue or disqualification.
But neither the added expectations nor her exertions in the 100m weighed Asher-Smith down as she cruised to a huge margin of victory over American Brittany Brown, who won silver, and Switzerland’s Mujinga Kambundji, who took bronze.
“I don’t know what to say, I don’t think it’s properly sunk in,” Asher-Smith said immediately after the race. ”Jon [Blackie, her coach] and I knew I could do it. I woke up today thinking ‘this is it. This is the moment you did all your work for’. The tiredness disappeared.”
She added: “All the support means so much. For my mum, my dad and his wife to be here, it means so much. I’m lost for words. I dreamt of this and now it’s real.”
Asher-Smith becomes only the sixth British woman in history to become an athletics world champion, and will now set her sights on next summer’s Olympic Games in Tokyo.
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