At just 21, the Norwegian has already established a sense of inevitability reserved for the game’s top finishers.
With Dortmund already a goal ahead following a spectacular 10th-minute volley from Raphael Guerreiro, Haaland’s first came in midway through the first half.
Rising above two defenders, Haaland met teasing cross from Thomas Meunier to lead an imposing header past goalkeeper Andreas Luthe.
Dortmund’s victory seemed assured as Union’s Marvin Friedrich turned Marco Reus’ withdrawal into his own net early in the second half.
However, a penalty from Max Kruse and a header from Andreas Voglsammer put the opposing team within reach of a stunning comeback, paving the way for a nervous 10-minute final for Dortmund.
Enter Haaland. Just minutes after Voglsammer’s goal, the forward rushed over a long pass from Mats Hummels, struggling with Union defender Robin Knoche.
With seven goals and three assists in just five Bundesliga appearances this season, Haaland is averaging two goals per game.
Seven high for Bayern striker frank
Robert Lewandowski continued his assault on the European football record books by becoming the first player to score in 13 straight home Bundesliga games, his 19th consecutive goal in all competitions.
Joshua Kimmich scored a brace, Leroy Sane, Serge Gnabry and Eric Maxim Choupo-Moting all got involved.
A self-defeating goal by Vasilis Lampropoulos from Bochum summed up a scorching day for the newly promoted team.
With a goal difference of +16 after just five games, Bayern occupy the top of the Bundesliga table with VfL Wolfsburg with 13 points and Dortmund chasing 12.