An early strike by River Plate's Mariano Pavone was not enough to save the Argentine juggernauts as they were relegated to the second division after only managing a 1-1 second leg draw against Belgrano in the play-offs.
Needing to win by two goals or more to stay in the Primera A after losing to Belgrano 2-0 in the first leg a week ago, River missed chance after chance to turn the tide as Pavone spurned a penalty kick in the second half.
Up 1-0 at halftime, the home side could not find the goal needed in the second half as a grave error by the River Plate defence saw all hope of remaining in the top flight evaporate.
Five minutes into the game, there was hope for the Monumental faithful as River took the lead to reduce the aggregate deficit to 2-1. After a disallowed goal by Belgrano for offside a minute earlier, Pavone, using his body to hold off a defender at the top of the box, received a long ball from midfield. The former Real Betis man turned towards the right of the box before firing a low shot perfectly into the bottom corner of the net to make it 1-0 on the night.
The stadium erupted with screams of excitement as the chance to stay in the top flight looked like more of a possibility.
Neither club managed to create attacking chances in the ensuing 20 minutes as an abundance of fouls hampered the pace of the game.
The referee then denied the home side another opportunity minutes later. River's Leandro Caruso, charging down the left side of the pitch near goal, cut into the box before looking to take the ball to the end-line with another cut. Claudio Perez went to stop Caruso, dropping him to the ground with a beastly tackle. What looked like a clear penalty, referee Sergio Pezzotta would have nothing of it, calling for a corner as the ball went out of bounds.
The first half ended at 1-0 to the home side. For the teams, the second half awaited as the future of both sides remained in a fragile state.
In the early part of the half, it was more of the same. River had possession and constantly went on the attack to find a second goal that would level the aggregate score. Belgrano were more reserved, looking to defend over attack, though counter-attacking was the team's priority.
Three minutes in, Belgrano's chance to bury their illustrious hosts came when Cesar Pereyra was sent though after a header passed the last line of the River defence. The shot landed a few metres wide of the right post as Belgrano fans held their heads in disbelief.
The disbelief was transformed into bliss as Guillermo Farre capitalised on an error by the River backline just minutes later. Juan Manuel Diaz went to clear a high ball heading towards the box, but failure to communicate with his team-mates resulted in the ball bouncing off Alexis Ferrero and landing in front of goal, where Farre drilled home a low shot under Juan Pablo Carrizo to tie the game with just under 30 minutes remaining.
Needing two goals, Pavone missed a penalty a minute later as Juan Carlos Olave got to the ground quickly to make the stop as Argentine's most successful domestic club was relegated for the first time in their history, causing chaos and mass rioting amongst the home fans at the Monumental.
For Belgrano, they will return to the top flight for the first time since 2006.