The 29-year-old bagged the third goal in the 3-0 victory against Weder Bremen, having last scored on October 31 last year against FC Augsburg.
BVB manager Niko Kovac revealed his satisfaction with the Guinea international's contribution and backs the goal to inspire the teams attack for the rest of the campaign.
"I am really happy of course for him [Guirassy]," said Kovak to the club website.
"Everyone knows that when you're a striker waiting for a goal, and it just doesn't happen, it feels especially good to score the 3-0 at the right moment, even more so when you come off the bench."
The goal was marked the strikers tenth goal of the season in all competitions after 25 appearances and keeps Dortmund in second spot on the Bundesliga table, four ahead of third placed RB Leipzig.
"We are a team. We're all there for each other, and I'm extremely happy for anyone who scores a goal. And at a moment like this even more so," added the Croatian mentor.
"It's important that he scored, not just for himself, but also for us as a team. Without goals, you don't win games, and you don't achieve your objectives."
The German giants will host FC St. Pauli at the Signal Iduna Park in Dortmund on Saturday.
RB Leipzig captain David Raum insists his side are ready to make Bayern Munich pay for their 6-0 drubbing five months ago as the Bundesliga giants visit the Red Bull Arena on Saturday.
Vincent Kompany praised his Bayern Munich players after their 3-1 win over FC Koln sealed a record-breaking first half of the Bundesliga season, but the coach was quick to stress that the real work was still to come.
Wednesday's Bundesliga matches saw Bayern Munich make history by equalling the best-ever first half of a season, while RB Leipzig climbed back into the top three.
Tuesday's Bundesliga action saw Borussia Dortmund tighten their grip on second place, headlining a trio of matches that shook up the top and bottom of the table.
