Thousands of Hong Kong football fans booed loudly and turned their backs when the Chinese national anthem was played before a World Cup qualifier match against Iran.
The move took the city’s months of protests into the sports realm.
The crowd broke out into Glory To Hong Kong, a song reflecting their campaign for more democratic freedoms in the semi-autonomous Chinese territory.
After the match started, fans chanted Fight For Freedom and Revolution Of Our Times.
One person carried a blue poster that read: “Hong Kong is not China.”
Hong Kong has been plagued by protests since June over an extradition bill that would have sent some residents to mainland China for trial.
The government promised last week to withdraw the bill but that failed to placate the protesters, whose demands now include democratic reforms and police accountability.
Fans were already chanting slogans as they streamed into the Hong Kong Stadium.
Security was tight, with fans frisked to ensure they did not bring in political materials and other prohibited items.
Iran, Asia’s top team, had sought to move the match, citing safety concerns over the unrest, but the request was rejected by Fifa, football’s governing body.
Stadium announcers said 14,000 spectators attended the game.
In July, Hong Kong fans chanted slogans and waved banners when English Premier League champions Manchester City played local team Kitchee at the stadium.
Many see the extradition bill as a glaring example of the city’s eroding autonomy since the former British colony returned to Chinese control in 1997.
Clashes have become increasingly violent, with police firing tear gas after protesters vandalised underground stations, set street fires and blocked traffic over the weekend.