Germany were reduced to 10-men after the half-hour mark and their coach believes his side's task was made all the harder by Argentina's all-star attack
After making a steady start to the match, the Hannover keeper received his marching orders for a professional foul on Jose Sosa and Die Mannscaft soon collapsed.
"We had 20, 25 very good minutes," he is quoted as saying by DFB.de. "But the red card took us by surprise and then also the goal.
"After that it was difficult for us against world-class people like Messi, [Gonzalo] Higuain or [Angel] Di Maria.
"We made some tactical errors, but the players gave their all.
"It is difficult to disrupt the opponent when you are outnumbered. In the first 20 minutes, we did it, but not later."
Sami Khedira scored an own-goal to set the Argentines on their way, and was quick to apologise to Germany fans for the gaffe.
"This result is ultimately deserved. But with a little luck, we could have got a draw. I'm sorry for the own goal. It was the first one I ever scored."