Dortmund dropped to 12 points behind runaway leaders Bayern Munich after Sven Schipplock and Kevin Volland fired Hoffenheim into a two-goal lead in the first half.
And although Dortmund won a point thanks to efforts from Pierre-Emerick Aubameyang and Lukasz Piszczek, Jurgen Klopp's men lost further ground on Bayern as a result after the champions beat Hamburg 3-1.
Bayer Leverkusen – who sit second – can go eight points clear of the third-placed Dortmund if they beat Eintracht Frankfurt on Sunday, and a dejected Sahin thinks it is Sami Hyypia's men they are chasing.
"No-one really cares about Bayern anymore and tried to compete," Sahin said after the draw.
"We have to make sure we catch Leverkusen."
Dortmund coach Klopp was not as forthright, but bemoaned his side's profligacy in front of goal.
Klopp's side dominated the second half but could not find a third goal, with Robert Lewandowski having a late effort spilled onto the post by Hoffenheim goalkeeper Jens Grahl in the dying stages.
"If you create that many chances, you deserve to win usually. It is our own mistake," he said.
"Other teams like playing against us and want to beat us. I would love if they wouldn't like us and we would be at the number one position."
Dortmund midfielder Sven Bender shared Klopp's view of the match and felt his side wasted their chances.
"We missed plenty of high-class chances, we kept missing coolness and weren't clever enough at the end," he added.
