The Tunisia international lashed a speculative drive past Jason Steele and tried to fire up the home crowd, even though his strike proved a mere consolation in the end, as the Seagulls retained their 3-1 advantage in the closing stages.
It represented a maiden United first-team goal for the 20-year-old, who got off the mark at senior level with a clever free-kick for Birmingham City during his loan spell with the Midlanders last term.
Speaking to MUTV's Stewart Gardner afterwards, Ten Hag was pleased with what he saw from the youngster, who played with spark and passion.