The electricity cut affected the historic centre of the Eternal City and the Vatican, halting the free metro service laid on for the all-night bash.
The cultural binge modelled on the highly successful festival organised last year for the first time in Paris.
City mayor, Walter Veltroni described the Roman version as a "token of love".
Paris Mayor Bertrand Delanoe accompanied by Veltroni went to a performance of a modern Romeo and Juliet at the Globe Theatre in the Villa Borghese park, where hundreds of people queued up.
They went on to watch Italian composer Lucio Dalla's Tosca and a concert by Nicola Piovani near the town hall.
"It’s the first White Night in Rome, we hope it will be followed by a long series and will become European," Veltroni said.
Delanoe showed even greater optimism. "White Nights in the whole of Europe, yes. Me, I would like to say in the entire world," he said.
Coinciding with the extravaganza, a large number of public and other institutions remained open till the morning. Public transport was free.
Gigantic traffic jams stood testimony to the event's large draw.
Participants included 51 art galleries, 24 museums, three university colleges, nine cultural institutes, several churches, the Cinecitta movie studios and the Olympic stadium.