Christian Pulisic scored the opener as Borussia Dortmund defeated Sportfreunde Lotte 3-0 on Tuesday to set up a DFB Pokal semifinal against Bayern Munich.
The third-tier side, playing at nearby Onsabruck after the first attempt to play the tie at home was postponed because of a frozen pitch, held out until the 57th minute.
But they were undone when two of Dortmund's promising teenagers linked up for the breakthrough.
Ousmane Dembele carried the ball towards the top of the box, then laid off for the onrushing Pulisic, and the 18-year-old American placed his shot between the keeper's legs for his third goal in his last four games.
Andre Schurrle doubled the lead on 66 minutes, lashing home on the volley after Raphael Guerreiro nodded a cross into the former Chelsea man's path.
Moments after Pulisic was substituted, Marcel Schmelzer provided Dortmund's third from a long-range free kick in the 83rd minute to put the game out of reach.
The result sets up an April semifinal clash at Bayern Munich, with the draw already taking place on March 1.