Iran's reformists have won all of Tehran's 30 seats in parliament, according to preliminary results for Friday's elections, marking a major boost for President Hassan Rowhani.
"With your votes you have made possible a new era and I bow to you in reverence," Rowhani wrote on his Twitter page.
It remains to be seen now how the tally will break down for the seats outside the capital. The vote count will be complete late Sunday or Monday at the latest, Iran's Interior ministry said.
But the sheer scale of the advances in the capital could indicate a parliament more friendly to Rowhani's reformist policies - such as further opening Iran to foreign trade following last year's landmark nuclear deal with world powers.
Young supporters of the president and reformists were already planning street parties in Tehran to celebrate the preliminary results of the vote, which saw 4,800 candidates run for 290 seats in parliament.
However, Mohammed-Resa Aref, one of the reformists' top runners and a big winner in Tehran, said that the planned celebrations would be postponed in observance of current religious holidays.
Interior Ministry data indicated that hardliner Gholam Ali Hadad Adel could be edged out of parliament, with the leading candidate for the fundamentalist conservatives set to take 31st place in Tehran, one spot behind what would be necessary to take a seat in the legislature.
With 30 of the 290 seats in parliament going to Tehran, the capital has the highest proportion of representatives, each of whom enjoys particularly weighty influence.
But Hadad Adel may still have a chance of winning a coveted Tehran post in a run-off, since all parliamentarians must win more than 25 per cent of votes in order to enter the legislature in the first round.
Unconfirmed media reports said that 65 per cent of seats in parliament could go to the reformists, while the hardliners held strong in loyal yet politically insignificant villages and towns.
Rowhani and key ally Akbar Hashemi Rafsanjani - a former president - were also leading the race for the Assembly of Experts, which selects the country's highest authority, the supreme leader.
Meanwhile, the hardliners' top candidate for that body, Ayatollah Mohammad Taghi Mesbah Yazdi, was unlikely to poll in the top 16 and therefore might not make the cut to represent Tehran in the 88-strong assembly.
"Whoever the public does not want must go. You cannot fight against it," Rafsanjani wrote on Instagram. The former president had previously been criticized as a dissident for supporting Rowhani's reform policies.
The results have come as a hard pill to swallow for hardliners close to the country's supreme leader, Ayatollah Ali Khamenei. Until now, they have always dominated the Assembly of Experts and, for the past 12 years, they have held a majority in parliament.
Around 33 million of Iran's 55 million eligible voters took part in the elections, which are seen as a potential turning point for the traditionally anti-Western Islamic Republic.