The red-shirted supporters, mostly young men, surged through the FIFA media center underneath the stands, pushing and shoving their way past journalists and TV crews toward a corridor they apparently thought would lead to the grandstands.
To get to the corridor, the fans broke down a temporary wall in one corner of the room, sending metal lockers crashing to the ground, according to Associated Press journalists. They then rushed back down the corridor in the other direction, sending parts of the same wall crashing down onto media work tables.
Security officials at the Maracana - where the final World Cup final will be held July 13 - were slow to react. They eventually contained the fans in a section of the corridor around 15 minutes after they first broke in.
FIFA said at least 85 fans were detained. Some were marched away in a line by security officials, their arms out in front of them and rested on the shoulders of the person in front.
Outside, riot police armed with stun guns forced dozens of the detained fans to walk single-file toward a holding area. There, the Chile supporters chanted and loudly complained about scalpers charging $1,000 a ticket for the game. "I traveled thousands of kilometers to get here!" one fan yelled, while others chanted "FIFA is a mafia! FIFA is a mafia!"
Asked how many guards should have been watching the entryway where the Chileans busted through, security guard Diego Goncalves said "about 20."
"I was the lone guy standing out there (near the entry to press center)," Goncalves said. "All of a sudden they knocked down the fence and just pushed their way through."
FIFA said the fans forced their way past security.
"Ahead of the Spain versus Chile match at the Maracana a group of individuals without tickets violently forced entry into the stadium, breaking fences and overrunning security," FIFA said in a statement. "They were contained by the security and did not make it to the seats."
In the joint statement, FIFA and Brazilian World Cup organizers said they "condemn these acts of violence."
The fans came extremely close to racing down a corridor that leads onto the field. But they apparently didn't know how close they were and came back toward the media room.
There, security guards eventually gained control of the situation, waving their hands frantically and ordering the Chile supporters to sit down in a large group before leading them away. Many fans covered their face with scarves containing Chile's logo as they were photographed and filmed by journalists.
After the fans broke in, security was beefed up, with long lines of heavily armed military police standing watch as thousands of fans lined up to get inside the stadium.
Rio's military police and state secretariat declined immediate comment on security and asked the AP to send questions via email. There was no immediate response.
AP Sports Writer Gerald Imray contributed to this report.