Referee Wolfgang Stark admitted he had got a key decision wrong as Borussia Dortmund's hopes of defending their Bundesliga title were hit by a controversial home defeat to Wolfsburg.
A controversial red card and penalty saw the game turn on its head after a Marco Reus free-kick had given Dortmund an early lead.
After 35 minutes, Wolfsburg's Dutch striker Bas Dost was played clear. His effort seemed to be blocked by Marcel Schmelzer's knee - but Stark gave a handball and sent off the Dortmund left-back.
Diego converted the penalty and then, four minutes from half time, a Naldo goal gave Wolfsburg the lead despite Simon Kjaer seeming to be in an offside position.
Controversy also surrounded the Dortmund equaliser, which came from a corner that should have been a goal-kick. From the corner, Lewandowski went down and Jakub Blaszczykowski scored from the spot, but Bas Dost rounded off a breakaway for Wolfsburg's winner.
"We have analysed the pictures after the game," Stark said. "On the pitch, it was clear for me: handball on the goal line, and that leads to a red card and a penalty.
"But looking at the TV pictures you can see it was not handball. It was an error of perception, a clear mistake by me, and I am sorry about it."
Stark said he would take a few days to think about his performance, adding: "I will look at the situation again, how this can happen and how to prevent it from happening next time. Maybe I was in the wrong position, or maybe I was somehow fooled into it."
Dortmund general manager Michael Zorc called the penalty decision "unbelievable", while coach Jurgen Klopp said: "I cannot rate this match after minute 35.
"I am very pleased with our performance, but it's a brutal result. We have the return leg in Wolfsburg and we will get those points back."
After Stark admitted his mistake, the German FA announced that Schmelzer would not be suspended, meaning he can play in Dortmund's final Bundesliga game of the year at Hoffenheim.