River Plate touched down in Madrid on Thursday morning for the eagerly anticipated Copa Libertadores final second leg at the Bernabeu, a day after opponents and eternal Buenos Aires rivals Boca Juniors landed in the Spanish capital.
Spanish police are calling the security operation for Sunday's match, which has been switched from River's ground to Real Madrid's home 10,000 kilometres across the Atlantic Ocean, the biggest ever for a game in Madrid.
More than 2,500 officers are expected to be on duty for the match, known as the "Superclasico" and regarded as one of the world's fiercest football rivalries.
The Paseo de la Castellana, which runs from the centre of Madrid to the stadium, will be closed off from 9am local time on Sunday as police divide the two groups of fans to prevent violence.
The game was originally scheduled to take place on November 24 but was called off after several Boca players sustained injuries when rocks were thrown at their team bus as it arrived at the Monumental stadium.
Conmebol, South America's football confederation, initially postponed the game by a day before calling it off again and switching it from the Argentine capital to Madrid, a move that has been met with loud protests from both clubs.
River have complained of losing home advantage Boca enjoyed in the first leg, which finished 2-2 at the Bombonera on November 11.
Boca, meanwhile, say they should have been awarded the title - South America's equivalent of Europe's Champions League - as a result of the violent attack on their players.
Boca arrived on Wednesday and with River joining them in the Spanish capital, both teams were expected to train on Thursday.
River were scheduled to train at at Madrid's Valdebebas training base late last night while Boca's squad were set to be put through their paces at the Spanish football federation's training base at Las Rozas, north-west of the capital.
The south American giants were initially opposed to proposals to play their decisive second leg in Spain.
Former Boca and Argentina midfielder Juan Roman Riquelme lashed out at the decision earlier this week, saying it would make it "the most expensive friendly in history".
"It won't be the same. No matter how much I want Boca to win it, I think the final has to be played in our country," he said.
"The way it is, makes it the most expensive friendly in history."
The move to another continent has not lessened interest in the fixture, however, with practically all tickets for the final at the 85,000-seat Bernabeu already snapped up.
The winners will secure the final berth for the December 12-22 Fifa Club World Cup in Abu Dhabi.
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