Luleå dominated in the first period and a free-spirited Phoebe Staenz put 1-0 up after one minute.
Brynäs admitted a few minutes later, but the joy lasted only 24 seconds before Nicoline Jensen gave Luleå the lead again. The Northern Bots had 3-1 after the first period, but Brynäs would rise after the heavy start.
Erika Grahm reduced in the second period but the Luleå players protested wildly, saying that she slowed the puck with one skate. Maja Nylén-Persson then acknowledged at the beginning of the third period and then the match felt completely open.
It was 52.25 when Brynäs Johanna Olofsson hit a headless pass in his own zone, right in the gap on Phoebe Staenz who put 4-3 to the away team.
Brynäs chased a receipt and hit the post in the final minute, but the mistake was decisive and thus Luleå took home the first semi-final in the best of five.
The second semi-final will be played on Saturday at 19.00 in Luleå.