Corner ball. Esteban Andrada is up for it - the keeper. He stays there as River clear and Boca put it back in the mixer.

Fernando Gago then smashes a volley from 30 yards that Franco Armani does really well to hold.

Overload. River have four players over and Boca the one defender who gets a toe on it and diverts to his keeper.

With the rest of his side up the pitch Esteban Andrada throws the ball down and sprints up the park 20 yards past the watching River forwards who still must be thinking how they did not sink their rivals for good just now.

Franco Armani is down apparently injured now too. It's cramp - the physios are stretching his legs.

Time is trickling away for Boca, who have led three times over the course of these two legs, but are now seven minutes from defeat.

Here comes Carlos Tevez. TEN minutes for him to change things. Julio Buffarini taken off.

Just moments before, Camilo Mayada almost heads past his own keeper, Franco Armani reacting so quickly to stoop down and scoop up.

Two Boca players come sliding in, bodies on the line, to block a River Plate runner on the edge of their box. This is becoming primal now. There's not much else for these humans to run on.

Arms waving in that inimitable Argentine style in the stands - hanging loose as they manically draw up toward the sky and back down, repeat.

These could well be the biggest 15 minutes in these clubs' histories.

Half-time in extra time. Fifteen minutes to play and then it is penalties.

It's all River - as well you might expect. Boca hanging on to this, one shot at the most precious of prizes, by their fingernails.

A minute added on at the end of this first half in extra time.

Julian Alvarez tries a first-time effort from a smart short cut-back to the near post. The 18-year-old River substitute is keen to make his mark but this one is always swinging wide.

Juan Quintero takes another wild pop from range. It's way over the target. Boca's fans raise the volume in the stadium. There are a lot of nervous voices in play.

Esteban Andrada got a bit of a spray on his shin and he seems happy enough to carry on with that. The alternative would be going off and leaving his team with nine men and no recognised keeper.

Perhaps - perhaps! - there was a strategic element in his going down for treatment there.

Corner River. Roars from the fans behind the goal they are attacking. Everyone is on their feet.

Gonzalo Martinez swings in to the near post. It's cleared out to Juan Quintero who smashes an effort way over the bar.

Boca keeper Esteban Andrada has gone down with an apparent injury. The physios are on the pitch.

River Plate make their switch.

Exequiel Palacios comes off to be replaced by Julian Alvarez. Fresh legs up front. Two very different game-plans from here.

Winger Sebastian Villa walks off the pitch slowly. Defender Leonardo Jara is coming on to replace him. Calm down, he gestures with his open hands held out to face the grass.

How the complexion of this evening has changed since Dario Benedetto's marauding opener. Was it a mistake to take him off when Boca did?

River come forward again but Cristian Pavon picks up the poked clearance and drives up the field. The game is stretched now. Boca have to still go for it when they can.

Wilmar Barrios trundles off. Does his team play for pens now? They have one change left to make and it may well be a defensive one rather than Carlos Tevez.

It's a zippy start from River but both sets of players must be suffering now - we already saw Nahitan Nandez's epic battle with cramp.

Boca's Wilmar Barrios is off! A second yellow card for this studs-up challenge on Exequiel Palacios right under the ref's nose.

Back under way. Here we go.

Right, as you've brought it up David. I've been reliably informed that the most likely explanation for indirect-free-kick-and-not-penalty-gate is that the referee must have decided the River defender was guilty of dangerous play - by raising a boot - without actually committing a foul. That, apparently, is a thing.