Free-kick River. Lisandro Magallan with a late sliding challenge just outside the area - it was wild but early in the game, no card.

It's swung towards the far post where Carlos Izquierdoz scrambles behind for a corner. Boca clear, but only as far as River's impressive number 10 Gonzalo Martinez. Not so impressive here as he dribbles straight out of play.

I can hear more Boca songs than River ones at the moment. It's loud.

Boca's Pablo Perez takes three tumbles clutching his ankles after a late challenge. He was one of the players injured in the River fans' bus attack.

As you can imagine, this has been a lively start.

We're off!

So almost a month after the first leg at Boca's ground, 6,000 miles away from Buenos Aires, the second leg of the Copa Libertadores final - the Superfinal - is about to get under way...

Electricity in the air.

A few more points of order to mention before kick-off. River's manager Marcelo Gallardo is serving a touchline ban, so we'll not see much of him.

There do look to be some empty seats high in the stands but I can't say for sure whether that's not a strategy to contain the sets of fans.

More from Alejandro Dominguez: "We did not betray anyone. The decision of coming here was because of what happened in the Monumental stadium.

"In the future, everyone has to be responsible for their actions. River Plate had the chance (to play at home) and we had to make the decision that this match was going to be played and not decided in other ways.

"Governments around South America have to make decisions and even make new laws that would guarantee that football matches and other spectacles are safe from trouble-makers. I don't see this as something that Conmebol can solve alone."

The Argentina national anthem is being played in the Santiago Bernabeu. One of my favourites. The ground looks full. This will all sound amazing.

Conmebol president Alejandro Dominguez was speaking to BBC Sport on Saturday.

"There were so many countries and cities that proposed to us to go and have the game played there," he said.

"There was Miami, Medellin, Genoa, cities from Brazil, and I'm very thankful. But after all the analysis, we thought that Madrid was the city to come to.

"There are 350,000 Argentinean people living in Spain so we wanted to give the opportunity to them to live this match and feel it.

"And the Bernabeu Stadium is like the Mecca of football in the world."

Interestingly, because we go into this match level on aggregate and away goals don't come into play, this is essentially a one-off match at a neutral venue. Which is exactly how the final will be decided from next year.

Although they probably won't end up playing it in Spain. Maybe it'll be Qatar instead...

Lionel Messi is in the house - get caps lock on.

Here's how the two teams line-up. Carlos Tevez only makes the Boca bench.

Boca Juniors XI: Andrada; Buffarini, Magallan, Izquierdoz, Olaza; Perez, Barrios, Nandez; Pavon, Benedetto, Villa.

Subs: Rossi, Goltz, Jara, Gago, Abila, Zarate, Tevez.

River Plate XI: Armani; Montiel, Maidana, Pinola, Casco; Ponzio; Fernández, Palacios, Perez, Martínez, Pratto.

Subs: Lux, Quarta, Zuculini, Quintero, Mayada, Mora, Alvarez.

More possibilities:

We could be in for a brilliant match of actual football. Aside from the emotion and gravity of the occasion, both teams have got some very good players, too.

It's worth keeping an eye on Cristian Pavon for Boca - we was part of Argentina's World Cup squad.

River's Gonzalo Martinez also plays for Argentina and shone in the first leg - a pulsating 2-2 draw at Boca's La Bombonera (the name means The Chocolate Box).

There is one flashpoint moment that has brought us here of course. The River fans' attack on the Boca team bus before the second leg.

It is what led to Conmebol (South American football's governing body) postponing the match twice, because at first they said it would be played the next day, before changing their mind.

Boca are still arguing - at the Court of Arbitration for Sport (Cas) - that River should be thrown out over the incident.

Incredibly, Cas have still not announced a ruling on that. So in theory, we could be in a position where River beat Boca tonight but end up having the title taken off them. There's been no indication what Cas will decide, it's just a possibility.

It is hard to press home just how big a deal this match is in Argentina and in Buenos Aires especially. The country's two biggest teams have a long history of fiercely contested derby encounters.

For example. When they met in the Copa Libertadores last 16 in 2015, Boca fans cut holes in the players' tunnel and sprayed pepper gas at the River Plate team as they were coming out for the second half.

The match was abandoned, and Boca were thrown out of the competition.

So of course the scrutiny, the tension, the excitement was going to be high around this, the first meeting between the two teams in the final of what is the South American equivalent of the Champions League.

It's all been amplified seemingly beyond maximum levels, and has led us to these alien conditions in the Spanish capital.

Image source, Getty Images

Where to begin? Even by Argentinean football standards, this match is being played in truly bizarre circumstances.

There have been delays, controversies, a bus attack and now a new setting, 6,000 miles away on a different continent.

A few weeks ago we were all looking forward to what was supposed to be a brilliant occasion. It was the decisive second leg of South America's biggest club competition. It was between two teams who share arguably football's most intense and passionate rivalry. It was delicately poised at 2-2

Instead this second leg is being played 15 days later than was scheduled, and in Madrid, a long way from Buenos Aires, the city that owns this rivalry, both the good and the bad.