A common space for harmonic peacemakers
Thousands of Thai protesters seized control of a satellite transmission station, forcing officials to allow an opposition TV channel back on air.
Security forces retreated after their efforts to disperse the crowd with tear gas and water cannon failed.
The government had shut down the People Channel on Thursday under state of emergency laws, and now says it will act again if it "distorts information".
The clash follows a month-long protest aimed at forcing early elections.
The demonstrators were angry at the government's decision to close down the channel, which the authorities have accused of inciting violence.
In defiance of emergency law, the red-shirts seized control of a building in the ThaiCom compound, intent on restoring the signal of the People Channel (PTV), which has proved an effective tool in drawing thousands of extra protesters into Bangkok.
The security forces tried to defend the compound, using first water cannon then tear gas but were eventually driven into retreat by the protesters.
PTV returned to air after talks between police and protest leaders, prompting the crowd to withdraw.
An official said the signal remained under government control.
"We are still controlling any news reporting that distorts facts," Panitan Wattanayagorn was quoted by the Associated Press as saying.
The BBC's Rachel Harvey, who is at the scene, says the red-shirts have won this round, but their goal of early elections is as elusive as ever.
The government remains resolute despite this humiliation, she says.
This was the first time during the current stand-off that the government has used force against the protesters.
Several red-shirts and police were reported injured.
Earlier, in a televised statement, a spokesman for the Thai military said it was prepared to use light to heavy means to hold back the protesters.
If the red-shirts failed to heed warnings, he said, batons, tear gas and rubber bullets would be used.
The red-shirts began their campaign on 12 March, establishing two camps in Bangkok - one at Government House and another in the commercial district, forcing some businesses to close.
The red-shirts - many of whom are sympathisers of ousted leader Thaksin Shinawatra - want Prime Minister Abhisit Vejjajiva to resign and call elections, saying his government is illegitimate.
They have vowed to defy the emergency laws with more rallies.
Arrests warrants have been issued for several of the protest leaders.