TEHRAN — Iran's reformist-backed presidential candidate surged to a wide lead in a partial vote count Saturday, a top official said, suggesting a flurry of late support could have swayed a race that once appeared solidly in the hands of Tehran's ruling clerics.

An Iranian woman casts her ballot for the Iranian presidential election at the Iranian Consulate in Kerbala, 110 km (70 miles) south of Baghdad, June 14, 2013. [Photo/Agencies]

The powerful showing by former nuclear negotiator Hasan Rowhani, which may be enough to give him an outright victory and avoid a two-person runoff next Friday, demonstrated the strength of opposition sentiment even in a system that is gamed against it. The ruling clerics barred from the race reform candidates seen as too prominent, allowing a list of hopefuls who were mainly staunch loyalists of the supreme leader.

But the opposition settled on Rowhani as the least objectionable of the bunch, making him the de facto reform candidate.

While Iran's presidential elections offer a window into the political pecking orders and security grip inside the country — particularly since the chaos from a disputed outcome in 2009 — they lack the drama of truly high stakes as the country's ruling clerics and their military guardians remain the ultimate powers.

Security forces also are in firm control after waves of arrests and relentless pressures since the last presidential election in 2009, which unleashed massive protests over claims the outcome was rigged to keep the combative Mahmoud Ahmadinejad in power for a second and final term. He is barred from seeking a third consecutive run. However the last-moment surge around Rowhani injected some excitement in the race.

Rowhani had just over 50 percent of the more than 27 million votes tallied by mid-afternoon, the Interior Ministry reported, well ahead of Tehran Mayor Mohammad Bagher Qalibaf with about 15.8 percent. Conservative Mohsen Rezaei and hard-line nuclear negotiator Saeed Jalili were running neck and neck at third place.

Minister Mostafa Mohammad Najjar said the final result would be announced by late Saturday. Iran has more than 50 million eligible voters, and turnout in Friday's election was believed to be high.

Election officials began the ballot count after voters waited on line for hours in wilting heat Friday at some polling stations in downtown Tehran and other cities, while others cast ballots across the vast country from desert outposts to Gulf seaports and nomad pastures. Voting was extended by five hours to meet demand, but also as possible political stagecraft to showcase the participation.

The apparent strong turnout — estimated at 75 percent by the hard-line newspaper Kayhan — suggested liberals and others abandoned a planned boycott as the election was transformed into a showdown across the Islamic Republic's political divide.

On one side were hard-liners looking to cement their control behind candidates such as Jalili, who says he is "100 percent" against detente with Iran's foes, or Qalibaf, who was boosted by a reputation as a steady hand for Iran's sanctions-wracked economy.

Opposing them were reformists and others rallying behind the "purple wave" campaign of Rowhani, the lone relative moderate left in the race. Many reform-minded Iranians who have faced years of crackdowns looked to Rowhani's rising fortunes as a chance to claw back a bit of ground.

Iran has no credible political polling to serve as harder metrics for the street buzz around candidates, who need more than 50 percent of the vote to seal victory and avoid a runoff. Journalists face limits on reporting such as requiring permission to travel around the country. Iran does not allow outside election observers.

The Interior Ministry said Rowhani had 14,020,139 votes from the 27,594,719 counted so far. Qalibaf trailed with 4,369,985. Jalili had 3,163,211 and Rezaei 3,129,444. The other two candidates were far behind.

Officials did not say in which parts of the country the ballots were counted. Counts tend to come in first from provinces outside the capital, raising the possibility ballots from Tehran could tilt the decision.