Hertha moved to within just three points of their third-placed visitors, who took the lead through Salomon Kalou and won the game with Marvin Plattenhardt's stunning second-half free-kick.
Pierre-Emerick Aubameyang's strike had drawn Dortmund level, but Tuchel felt his side created enough chances to win the game at the Olympiastadion.
Gonzalo Castro and Aubameyang were both guilty of missing opportunities following the former's equaliser, while Andre Schurrle spurned a glorious early opening.
"We had two good opportunities to go ahead and then we gave them a goal," said the Dortmund coach. "Our lack of effectiveness cost us the three points.
"The same performance would have been sufficient here more often than not. The result is annoying, but the performance was okay."