Tijuana, a northern Mexican border town side punching well above their weight in South America's elite club competition, advanced to the quarter-finals 2-1 on aggregate after they were held to a 0-0 draw in the first leg at the Caliente.
Things will not get any easier for the Mexican underdogs in the last eight, however, as the victory set up a showdown against Ronaldinho's Atletico Mineiro, who are firm favourites to win the title for the first time.
For Palmeiras, the dream of winning the trophy for a second time after their 1999 victory is over and, having been relegated last year, they must make do with concentrating on fighting for promotion from Brazil's second division.
Bruno let Riascos's weak shot slip through his grasp and into the net in the 27th minute of the last-16, second leg at the Pacaembu in Sao Paulo.
"It was a grotesque mistake that shouldn't have happened. It was my fault, the first goal was critical for the defeat," Bruno told reporters.
In a match littered with fouls, Venezuelan referee Juan Soto also blundered when he sent Tijuana defender Richard Ruiz off for what he thought was a second yellow card offence before realising he had not previously booked the player and called him back.
Tijuana-born midfielder Fernando Arce increased the away side's lead early in the second half before being harshly penalised when the ball hit his hand and Palmeiras pulled a goal back with Souza's spot kick in the 61st minute.
Paraguayan defender Pablo Aguilar was then sent off, leaving Tijuana a man short for the last seven minutes but that did not dampen the team coached by Argentine Antonio Mohamed's joy at qualifying.
The Mexicans, who won their first league title in December, are the second side founded this century to reach the last eight after Peru's Real Garcilaso.
Garcilaso, formed in 2009 two years after Tijuana, upset three times South American champions Nacional of Uruguay on penalties last week.
- Sports & Recreation
- Atletico Mineiro