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The 23-year-old crossed the line in 10.88 seconds to beat double Olympic and seven-time world champion Fraser-Pryce, with Ivorian Marie-Josee Ta Lou squeezed out into third place.
Asher-Smith will bid to seal a 100m and 200m sprint double at the 2019 World Championships later this month - and this was the perfect performance before heading to Doha.
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Having finished second in the 200m at the Diamond League final in Zurich last week, she went one better to light up the Belgian capital.
Olympic 400m champion Shaunae Miller-Uibo edged her out of first place in Switzerland, and despite another season's best on that occasion, the Briton bolstered her world medal claims with a first Diamond League title in Brussels.
Meanwhile, American Noah Lyles completed a sprint double with victory in the 200 metres to add to last week's 100 title before he seeks to be crowned world champion for the first time later this month.
Lyles was pushed by Turkey's Ramil Guliyev and Canada's Andre de Grasse, with both running season's bests. Lyles, 22, had talked on Thursday of wanting to improve on his personal best on Friday, but on a cold wet night in Brussels he had to settle for a still respectable 19.74 seconds.
In a photo finish, Guliyev came second, just ahead of De Grasse. American Lyles has broken through in the past two years.
He bettered Usain Bolt's Paris Diamond League record for 200 metres last month and will run only the longer sprint in Qatar, saying he is not so strong over the shorter distance.
Lyles did though win the 100 in the first leg of the Diamond League finals in Zurich last week.
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