The yellow card came in the 88th minute and was Schüller's third in total, which means a suspension for the next match.
The midfielder showed great frustration and took to his forehead afterwards when he realized what the consequence was.
Djurgården has otherwise shone in the Europa Conference League, with tonight's result winning six out of five games in the group stage, and securing second place in the Allsvenskan before the final round.
The winning goal of the evening came in the first half when Magnus Eriksson both initiated the attack and finished it.
Elias Andersson was responsible for the post from the left wing, which Kalle Holmberg unselfishly played on to the DIF team captain with a short pass.
The goal was a bit lucky, as Shamrock's goalkeeper was positioned correctly and was on the ball, but a little fumbled the ball under him into the net.
Shamrock is otherwise the only team Djurgården did not manage to defeat in their group F (the meeting in Dublin ended 0-0).
The round of 16 will be played on March 9 and 16 next year.
Which team will meet will not be clear until February, when the group twos in the Europa Conference League meet the group threes in the Europa League playoffs.