Dortmund were finding it difficult to get a foothold in the game up to this point, with the likes of Marco Reus finding it difficult to get throught the Frankfurt defence.
The moment to change that came in the 36th minute.
A corner from Larson from the left wing was swung in to the danger area.
The ball fell to Diallo, who headed it twoards goal and desite the opposition keeper saving it, he followed up to squeeze the ball in to the net and give Dortmund the lead.