Iran's presidential race lost one more candidate Tuesday but gained a new script: reformist leaders uniting behind relative moderate Hasan Rowhani to boost his once-improbable shot at victory.

Former presidents Mohammad Khatami and Akbar Hashemi Rafsanjani fell behind Rowhani after a rival moderate bowed out in attempts to consolidate reform-minded forces battered by years of crackdowns.

The move forced hardliners and conservatives favored by the ruling clerics to consider anointing their own unity candidate or risk having Friday's election slip away.

"Rowhani now has the best situation among the candidates," said Saeed Leilaz, a Tehran-based political analyst. "He will win the election on Friday."

But reformists still have major challenges ahead following former Vice President Mohammad Reza Araf's withdrawal from the presidential race.

Rowhani's backers must persuade their flock to go to the polls rather than boycott a vote many allege to be unfree and unfair. Iran's election overseers last month pruned the list of would-be hopefuls to eight candidates, most of them loyalists favored by both the theocracy and the military.

Among those cut from the candidates list was Rafsanjani, angering many reformists who believed only he had the stature to defeat the hardliners. Rafsanjani praised Aref's decision to withdraw in favor of his protege, Rowhani.

"Rafsanjani was really the only choice to re-energize reformists," said Rasool Nafisi, an Iranian affairs analyst at Strayer University in Virginia. "Rowhani only got their support because he is seen as Rafsanjani's man and a vote for Rowhani was a vote for Rafsanjani."

Rowhani, a 64-year-old cleric and former nuclear negotiator, rejects outgoing President Mahmoud Ahmadinejad's combative approach in world affairs and sides with Rafsanjani's view that Iran can maintain its nuclear program and ease tensions with the West at the same time.

Although all key decisions in Iran are ultimately in the hands of the ruling clerics, Rowhani's ties to the influential elder statesman Rafsanjani could give him more latitude to sway viewpoints if elected president.

But a significant number of opposition backers also say they are now more interested in a capable fiscal steward such as Tehran Mayor Mohammad Bagher Qalibaf as Iran's economy sinks under international sanctions and alleged mismanagement.

And more hardline candidates could well pull out of the race and rally around one of their own, such as current nuclear negotiator Saeed Jalili. Rowhani currently is set to face off against five conservative candidates including Jalili.

Beyond shaping the candidates' list, Iranian authorities also have kept an extremely tight lid on any possible dissent. They keep close watch for impromptu political rallies and try to choke off the Internet and foreign-based satellite TV channels such as the BBC and Voice of America.

Nevertheless, Hamid Reza Shokouhi, an editor at the pro-reform Mardomsalari newspaper, said Aref's withdrawal could boost turnout.

"It not only will move his supporters in favor of Rowhani, but it will also convince disappointed voters who didn't want to vote," said Shokouhi, adding that many had planned to boycott since "they saw no chance for either Aref or Rowhani to make it to the run-off because of the vote split."

Reactions were mixed, though, among a small sampling of pro-reform voters on the streets of Tehran.

Morteza Moradpour, a student, said "Aref's withdrawal can boost reformists very much because now reformists have one joint choice and can run more unified."

But Rahim Kazemi, a shopkeeper, said, "We would love to see Aref in the race because if there were a runoff he stood a better chance. I think now that he has withdrawn from the race many may not go to ballot boxes."

Under the Iranian system, if no candidate gets a majority in the first round, then the top two have a run-off.

The election will choose a successor for Ahmadinejad, who under the law cannot run for a third term. It is also a major test for Iran's clerically dominated establishment after Ahmadinejad's disputed 2009 re-election. That vote unleashed the worst domestic unrest since the 1979 Islamic Revolution. Many university students and other reformists remain imprisoned following a massive crackdown.

In his campaign stops, Rowhani has been careful not to confront authorities directly over the crackdown. But he has called for police to stop harassing women over their choice of clothes in public, and for restoring the dignity of universities and its students.

"Rowhani will let women have a greater role and freedom in society," said Shohreh Ghasemi, a nurse in Tehran. "Other candidates just urge women to sit at home waiting for to deliver another  baby."

Rowhani represents an important test for Iran's broad spectrum of alternative voices, ranging from moderates who want less confrontation with the West to hardened opposition groups at odds with the Islamic system as a whole.

Rowhani has tried to keep his message broad, arguing that less confrontational policies would allow Iran to advance its nuclear program while easing Western concerns and allowing for sanctions to be rolled back.

The West and its allies fear Iran could be moving toward development of a nuclear weapon. Iranian officials, including Rowhani, insist that the country seeks nuclear reactors for energy and medical applications only.

Rowhani served as Rafsanjani's top national security adviser during his 1989-97 terms as president.

He took over the nuclear portfolio in 2003, a year after Iran's 20-year-old nuclear program was revealed. Iran later temporarily suspended all uranium enrichment-related activities to avoid possible sanctions from the U.N. Security Council.

Ahmadinejad strongly opposed any such concessions and deal-making, which took place while Khatami was president.

Rowhani, who backed Rafsanjani's unsuccessful candidacy in the 2005 presidential race, resigned as nuclear negotiator after a few testy meetings with the recently elected Ahmadinejad.

In a statement Tuesday after Aref's withdrawal from the race, Rowhani said he feels more responsibility to continue "reforms and moderations."

Aref said on his website that he made the decision to withdraw at Khatami's urging. He said Khatami told him that his continued candidacy "is not in the interest" of Iran's reformers.

Khatami then released a message thanking Aref, calling him "dear brother" and urging all reformists vote for Rowhani. "I will give my vote to his excellency the esteemed brother Rowhani. And I ask all reformists to see the presence of Rowhani (in the race) as an opportunity for achieving their demands."

Khatami is considered a father of Iran's reform movement, and Aref has been a close ally of Khatami's since his presidency from 1997 to 2005.

Rowhani also won an endorsement from Zahra Mostafavi, the daughter of the late founder of the Islamic Republic, Ayatollah Ruhollah Khomeini.