Haaland scored a stunning 20-minute treble after coming off the bench in his side's victory over Augsburg.
The striker, who was heavily linked with Manchester United this month, only entered the fray in the 56th minute before finding the net with his first touch three minutes later.
Dortmund had trailed 3-1 when Haaland was introduced but eventually ran out 5-3 winners.
BVB boss Lucien Favre said: "Erling has settled in well and immediately showed his strengths by making runs in behind.
"He moves very well between the lines and offers us other possibilities in our attacking play."
"If it becomes the same kind of success story, I'd be all for that. Erling is making a good impression and he got off to a superb start today."