Many took part in mourning processions as they gathered at the 75,000-capacity Azadi.
Iranian football fans faced a tricky balancing act Tuesday as they watched their team win against South Korea during a religious holiday in which they were banned from expressing joy.
Many took part in mourning processions as they gathered at the 75,000-capacity Azadi ("freedom") stadium in Tehran to mark the eve of Ashura, one of the holiest days in the Iranian calendar.
For Shiite Muslims, Ashura marks the death of Prophet Mohammed's grandson Imam Hussein in the seventh century, and is traditionally a day of sombre processions through the streets, in which black-clad men beat their chests and heads in anger and despair.
So it proved controversial with religious leaders when the Asian Football Confederation (AFC) match against South Korea was scheduled for the day before.
"Bear in mind that if football is going to be played on the eve of the Ashura, the atmosphere of this match must be 100 percent in line with Ashura," warned Friday prayer leader Ayatollah Ali Movahedi Kermani last week, according to the ISNA news agency.
"The entire stadium must be covered in black and shouts of Hussein must be heard constantly from the crowd. Instead of the clapping in these games, all should shout 'Ya Hussein'," he said.
The game, broadcast live on state television, showed a solemn black stadium packed with subdued spectators wearing black.
Iran beat South Korea 1-0 with Sardar Azmoun's goal 24 minutes into the first half.
Two big signs installed in the Azadi complex read in English "Hussein, the ark of salvation" and "Hussein, the everlasting voice of justice".
Between the two halves, religious singers came on the field and performed solemn religious songs about Imam Hussein.
Two enormous black flags with Hussein's name were unfurled inside the stadium.
"Spectators and players of both countries have been briefed to observe religious codes," General Alireza Adeli, the interior ministry's police chief, told the Tasnim news agency before the match.
The AFC is highly sensitive to expressions of religious devotion during games and had asked for the black flags to be removed.
"We won't do that. The Hussein banners are people's beliefs," said Iranian football official Mohammad Reza Saket, promising to pay any resulting fines.
South Korean journalists said they would voluntarily wear black arm bands to show respect for the holy day.
The game was a qualifier for the 2018 World Cup, and South Korea failed to break a 42-year losing streak in Tehran.