Persian hip-hop thumps from car speakers and young hipsters - men with spiked hair and women in spike heels - dance in the streets.
It's another night and another campaign rally-turned-party for their unlikely hero: a self-styled reformist from the early years of the Islamic Revolution who is now seen as their best hope to defeat hard-line President Mahmoud Ahmadinejad.
But while Mir Hossein Mousavi generates the noise, passion and electricity in Tehran, Ahmadinejad has the backing of the powerful Islamic establishment and deep support in the countryside, leaving Friday's vote too close to call.
Mousavi would appear to have the momentum, drawing staggering crowds and all-night street bashes. But all that noise, fervor and electricity doesn't necessarily add up to a juggernaut, with critical stakes at play, including possible talks with Washington after a nearly three-decade diplomatic estrangement.
The post-midnight raves in Tehran's leafy suburbs are uncorking passions that seem to have caught even Mousavi by surprise. He stood in awe Monday at one end of a nearly 12-mile human chain of supporters along one of Tehran's main thoroughfares, linked by green ribbons and banners in the symbolic color of his campaign.
What's left in the final days before the vote is a flat-out political end game that's fundamentally rewritten the rules of Iranian campaigns. This time, the attacks have been nastier, the crowds wilder and the media war more acute than any previous presidential race.
"A month ago, I would have said Ahmadinejad was a sure bet," said political analyst Sharif Emam Jomeh. "There was apathy especially with the youth. But now, until 3 a.m., they are out in numbers and they care ... Below the surface, something was boiling."
At stake is the political identity of Iran's highest elected official - and whether the next president will challenge or reinforce clerical influence on the state.
The non-elected clergy around Supreme Leader Aytollah Ali Khamenei hold most keys to power and dictate major decisions over internal security, justice and foreign relations. There is little real possibility to chip away at their constitutional clout. The presidency is the closest the voters can get to altering the direction of the country.
Mousavi's backers are hungry to recapture the energy and possibilities of a decade ago, when Khatami opened the way for greater freedoms that included liberal media voices and a softer touch with outreach to the West.