The Foals were under pressure for 80 minutes of the game at the Borussia Park Stadion on Saturday only to score twice in the final 10 minutes to inflict the first defeat of the season on Dortmund, reducing the deficit on their Westphalian rivals to six points as well.
"If you beat Dortmund 2-0 at home, then that's something," Favre said.
"Given the way the first half went, it's almost a miracle."
Favre admitted his side had been lucky to come away with a win, especially after a first half in which Dortmund had 17 shots on goal to their one.
"It was very poor from us," Favre told Sky. "We slept and didn't play football. Dortmund pressed really hard.
"You could see our weaknesses and we've definitely got to improve and play better under pressure, not only the way we receive the ball but the way we think - it was too slow.
"When it's 0-0 at half time in a game like this, then you've got to think positive because it was a really catastrophic first half, or almost catastrophic because at 0-0 in football, anything's possible."
Dortmund coach Jurgen Klopp admitted his side only have themselves to blame for not extending their lead at the top of the Bundesliga with a win, especially in view of Bayern Munich's draw with Bayer Leverkusen.
"As long as your opponents aren't beaten, they have every chance," Klopp said.
"And they were not beaten, just wobbling. We should have finished them off, but then we let in two and this feels really humiliating right now."