Wolfsburg coach Steve McClaren was at a loss to explain how his side threw away a 3-0 lead to lose their second straight Bundesliga match this season.
Visitors Mainz recovered from a first-half onslaught to turn the tables on the 2009 Bundesliga champions and, thanks to a late winner, leave the English coach lost for words.
''It is hard to explain,'' he said. ''It is the first time this has ever happened to me, both as a player or as a coach. After going 3-0 up, we had everything under control and then the team just stopped playing football.''
The Wolves were good value for their 3-0 lead with new signing Diego making a perfect debut with one goal and one assist, but McClaren's first points in German football still elude him.
''We have got to get this setback out of our heads,'' he told the club's website. ''We saw that when (Edin) Dzeko and Diego combine together, they will be a problem for the Bundesliga. But we have got to also defend well.''
Mainz moved into a share of the Bundesliga lead thanks to their second consecutive win, having beaten Stuttgart last weekend, and their coach Thomas Tuchel insisted he never lost hope.
''Even at 3-0, I was not totally unhappy with the performance of my side,'' he said. ''I believed in my team at all times. This game was evidence of the great development of my team over the last year. All I can do today is praise my team in the highest of tones for what they did on the field.''