Viktor Elm headed the ball into Johannsson's path on the right as the USA international came forward into the box. He took a touch off his knee and put in a right-footed shot past the onrushing keeper. The goal helped shore up AZ's lead in the quarterfinal tie as the holders seek to defend their crown.
The Icelandic-American was also on the mark this weekend, scoring the second goal in a 3-0 defeat of NAC Breda.
Johannsson and the Cheese Farmers return to action Saturday when they face PSV at 2:45 p.m. ET.