Even a win by Rowhani would be more of a limited victory than a deep shake-up. Iran's establishment, a tight alliance of the ruling clerics and the ultra-powerful Revolutionary Guard, still holds all the effective power and sets the agenda on all major decisions such as Iran's nuclear program and its dealings with the West. The greater comfort level by the theocracy and Revolutionary Guard also sets a different tone from 2009. Opposition groups appear too intimidated and fragmented to revive street demonstrations.

Rowhani, the only cleric in the race, led the influential Supreme National Security Council and was given the highly sensitive nuclear envoy role in 2003, a year after Iran's 20-year-old atomic program was revealed.

"Rowhani is not an outsider and any gains by him do not mean the system is weak or that there are serious cracks," said Rasool Nafisi, an Iranian affairs analyst at Strayer University in Virginia. "The ruling system has made sure that no one on the ballot is going to shake things up."

Yet a Rowhani victory would not be entirely without significance either. It would make room for more moderate voices in Iranian political dialogue and display their resilience. It also would bring onto the world stage an Iranian president who has publicly endorsed more outreach rather than bombast toward the West.

The last campaign events for Rowhani carried chants that had been bottled up for years.

Some supporters called for the release of political prisoners including opposition leaders Mir Hossein Mousavi and Mahdi Karroubi, both candidates in 2009 and now under house arrest. "Long live reforms," some cried at Rowhani's last rally. The rally was awash in purple banners and scarves — the campaign's signature hue in a nod to the single-color identity of Mousavi's now-crushed Green Movement.

"My mother and I both voted for Rowhani," said Saeed Joorabchi, a university student in geography, after casting ballots at a mosque in west Tehran.

In the Persian Gulf city of Bandar Abbas, local journalist Ali Reza Khorshidzadeh said many polling stations had significant lines and many voters appeared to back Rowhani.

Just a week ago, Rowhani was seen as overshadowed by candidates with far deeper ties to the current power structure: Jalili and Qalibaf.

Then a moderate rival of Rowhani bowed out of the presidential race to consolidate the pro-reform camp. That opened the way for high-profile endorsements including his political mentor, former President Akbar Heshmi Rafsanjani, who won admiration from opposition forces for denouncing the postelection crackdowns in 2009. This, too, may have led to Rafsanjani's being blackballed from the ballot this year by Iran's election overseers, which allowed just eight candidates among more than 680 hopefuls.

Fervor remained strong for Rowhani's rivals as well.

Qalibaf is riding on his image as a capable fiscal manager who can deal with the deepening problems of Iran's economy and sinking currency.

Jalili draws support from hard-line factions such as the Revolutionary Guard's paramilitary corps, the Basij. His reputation is further enhanced by a battlefield injury that cost him the lower part of his right leg during Iran's 1980-88 war with Saddam Hussein's Iraq, which at the time was backed by the United States.

"We should resist the West," said Tehran taxi driver Hasan Ghasemi, who supported Jalili.

Iran's supreme leader, Ayatollah Ali Khamenei, has not publicly endorsed a successor for Ahmadinejad following their falling out over the president's attempts to challenge Khamenei's near-absolute powers.

Ahmadinejad leaves office weakened and outcast by his political battles with Khamenei — yet another sign of where real power rests in Iran. The election overseers also rejected Ahmadinejad's protege Esfandiar Rahim Mashaei in apparent payback. The usually talkative Ahmadinejad gave only a brief statement to reporters as he voted and refused to discuss the election.

Khamenei remained mum on his own choice even as he cast his ballot. He added that his children don't know whom he backs.

Instead, he blasted the U.S. for its repeated criticism of Iran's clampdowns on the opposition and the rejection of Rafsanjani and other moderates from the ballot.

"Recently I have heard that a U.S. security official has said they do not accept this election," Khamenei was quoted by state TV after casting his vote. "OK, the hell with you."

Iran's state media hailed the apparently high turnout as a boost for the Islamic Republic's political system.

"A great political epic has shocked the world," read a front-page headline in Kayhan Saturday. Khamenei had called for a "political epic," saying a high turnout would protect Iran against its enemies.

The economy, too, is under far more pressures than in 2009.

Western sanctions over Iran's nuclear program have shrunk vital oil sales and are leaving the country isolated from international banking systems. New U.S. measures taking effect July 1 further target Iran's currency, the rial, which has lost half its foreign exchange value in the past year, driving prices of food and consumer goods sharply higher.