The Bundesliga leaders were beaten by lowly Augsburg on Friday, much to the frustration of the Westfalenstadion boss with Bayern now three points adrift.
Lucien Favre bemoaned Borussia Dortmund's mistakes in their shock loss to Augsburg as the slumping Bundesliga leaders opened the door for Bayern Munich.
Dortmund's title bid suffered another damaging blow as Ji Dong-won's brace led hosts Augsburg to a 2-1 victory Friday.
Favre's Dortmund were unable to make the most of their opportunities, giving reigning champions Bayern the chance to move level on points atop the table if they beat Borussia Mönchengladbach on Saturday.
Reflecting on the result – a loss that left Dortmund with just one win in their past five Bundesliga matches – head coach Favre told reporters: "I think we played okay.
"We were dominant and had many chances. Five or six great chances. But we made unnecessary mistakes. Our opponent didn't have as many chances. We have to accept it, but it happened, unfortunately."
Not even the return of Marco Reus from injury could lift Dortmund, with the captain making his first Bundesliga appearance since February 2.
On Reus, Favre added: "We have to stay cautious with Marco Reus. We have to meter his minutes. It was the plan today for him to play 60 minutes.
"We will see in the next games how he handles it. Today we just didn't want to have a setback. We will keep an eye on him, how many minutes are good for him, if he maybe has to go out at halftime or something like that."