Ajax travelled to Germany seeking a victory after the first leg ended in a 0-0 tie the previous week, and they got off to a strong start. Nonetheless, the hosts were given a penalty in the 18th minute when the ball struck Calvin Bassey's arm inside the area. Robin Knoche's penalty attempt came within inches from being saved by Rulli, making the score 1-0. Rulli was not at fault for the opening goal, but he committed a grave blunder just before halftime when Josip Juranovic's shot slid under his arm to give the hosts a 2-0 lead.

Mohammed Kudus scored from a Steven Bergwijn cross just after the interval to make it 2-1, but the celebration was short-lived as Danilho Doekhi headed Union Berlin in lead 3-1. The Dutch centre defender, who graduated from the Ajax school, returned to terrorise his former team.