A court heard how the lawyer also forced his victim to give him oral sex at the event.
The Ukrainian-born lawyer targeted the drunk American man on the Kotzhugel, an infamous hill beside the beer tents where many drinkers go to sleep off a day's boozing.
The rapist, known only as Sergeii C due to German's strict privacy laws, was filmed by a pair of Spanish festival-goers, but the footage was not made publicly available.
When the festival goers initially saw Sergeii C, they thought he was robbing his sleeping victim during the attack at around 10pm on October 1 last year.
One of them told the court:
'He grabbed the victim in the leather pants at the front. 'We thought at first it was a robbery. But then he made clear movements that surprised us.'
The lawyer admitted his crime in court but said he could not actually remember the incident.
He said to the court:
'I had drunk at least six litres of beer. I cannot explain it to myself. I am not homosexual.'Sergeii C claimed he had developed a 'spontaneous affection' due to the amount of alcohol he had drunk. He added that he believed the victim had agreed, otherwise he 'would have never done it'.
Sergeii C, who testified at the district court with the aid of a translator, was given a two-year suspended prison sentence.