Trossard's goal was his first since the opening day of the season against Chelsea. It was a clever finish from the Belgian international and capped a fine flowing move from Brighton after good build up play from Pascal Gross and Alexis Mac Allister.
Tottenham, who were without their key striker Harry Kane who injured his ankle in midweek against Liverpool, lacked a cutting edge and energy.
Brighton fully deserved their victory and should have added a second at the end when Aaron Connolly, on as a second half sub, saw his effort from three yards blocked by Alderweireld.
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Brighton fully deserved their victory and should have added a second at the end when Aaron Connolly, on as a second half sub, saw his effort from three yards blocked by Alderweireld.