Coach Rudi Voller opted to field a strong line-up, in a bid to refine his starting XI for this summer's Championship, however they were four-down by the break.
Two goals in the space of two minutes had the home fans in raptures after Mihaita Plesan's opener was swiftly followed by Razvan Rat's effort.
Ionel Danciulescu bagged a brace before the break to seal the result, leaving Voller to contemplate what his side could gain from the remainder of the contest.
Things did improve after the break with Stuttgart keeper Timo Hildebrand making his international debut after being handed a chance due to Jens Lehmann's injury.
The 25-year-old almost kept a clean sheet in the second half, but Gabriel Caramarin spoiled his big night with a fifth with just three minutes remaining.
Stuttgart's on-loan defender Philipp Lahm did pull one back late on, his first-ever international goal, but it proved scant consolation for one of this summer's favourites.
Voller has opted for a settled squad after qualifying this Euro 2004, however the door may be open to others to land a seat on the plane to Portugal following this defeat.
