Another River Plate change-up.

Gonzalo Montiel off and Camilo Mayada on in his place. We've got just over 15 minutes of normal time to play.

So 3-3 on aggregate - no away goals remember. How likely is it that a second leg taking place almost a month after the first will go all the way to extra-time and penalties.

How about this for a shout: 2-2 (4-4) AET (33-34 on pens)?

River looking to capitalise straight away. They ping in two crosses in quick succession that the Boca players manage to field well enough to safety. Adrenaline coursing through their veins now. They are no longer protected, the Boca players. River can sense the momentum changing. You can hear it - it is loud.

Cristian Pavon gallops alone, forward on the break. He cuts inside and shapes to shoot...

A rising effort that soars off into oblivion.

Lucas Pratto, falling back in the box, cushions a header on target from a right-wing cross, but there's no zip to it, no persuasion. An easy save.

It's a little like this second half so far. The opening 45 were far more adventurous - from both sides. River will of course be far more concerned about that.

Gonzalo Martinez with a few nice touches as he brings River forward, but he soon has to turn back and look to help with Boca camped deep behind the ball.

Wilmar Barrios steals in and wins a free-kick near his own box to relieve some of the pressure.

A change for Boca.

Dario Benedetto, the goalscorer, is coming off now. He looks disappointed. Ramon Abila on in his place.

Richard Padula
BBC World at the Bernabeu

The Argentine commentators are going crazy! Are they watching the same match?

Half an hour to play. Boca have produced nothing so far this half.

Esteban Andrada is fine. He gets play restarted.

River have made a change. Juan Quintero, the Colombia midfielder, is coming on for Leonardo Ponzio in the middle.

River send a ball bouncing dangerously in the box. Out comes the keeper.

Striker Lucas Pratto gets there first, and he raises his boot to flick it up before landing crumpled on the deck. River want a penalty because Esteban Andrada got nothing of the ball.

The referee seems to have decided it's a free-kick for a high boot instead. Andrada is down getting treatment.

Lucas Olaza steps up and strikes the wall which after all that almost certainly wasn't 10 yards back where it should have been.

Free-kick Boca. Right on the edge of the box. Dario Benedetto wins it from a tight spot between two defenders.

The referee counts out the 10 yards but of course the Boca players want it further back. It takes ages!

Richard Padula
BBC World at the Bernabeu

World Cup winner Jorge Valdano is here in the press box, but to be fair there haven’t been many reasons for him to jump out of his seat.

A tense atmosphere in the River section of the stadium...plenty of worried looking faces amongst the fans.

The Copa Libertadores trophy is sitting proudly in a commentary box not far away from us and at the moment Boca are looking favourites to get their hands on it.

Just wide! A lovely one-two on the edge of the box sees Ignacio Fernandez pop up in a pocket of space, he takes a touch to set himself and fires a drive that whistles past the far post. Esteban Andrada wasn't getting anywhere near it.

Sebastian Villa gives the ball away in midfield but races back to cover on the right wing. River switch flanks and win themselves an early corner.

A huge half ahead for them. This is a bright start.

Whipped in towards Jonatan Maidana who out-muscles his marker but heads way over the bar.

And we are back under way in Madrid.

It was a nervy, cagey opening to the match, but that was a quality finish from Dario Benedetto to give Boca the lead.

Remember - away goals don't count. Boca are 3-2 up on aggregate with the biggest half in these clubs' histories about to begin...

Parth Mehta: The Santiago Bernabeu will never have and never will again witness an atmosphere like this.