Every game here represents a last chance for Lionel Messi.
He is still great, still feted, still globally adored. Given the times and his place in them, he may be the most recognizable person who's ever lived.
But his window of opportunity closes daily.
If he is ever going to establish himself as the greatest soccer player of all time, he has to do it now, in the next two weeks. There are signs everywhere that this will not be possible in four years' time. His future – the future of what might be the most universally beloved sportsmen in history – is now.
If Argentina leaves here without a trophy, Messi is cast off into that anteroom of legends, along with players like Cruyff, Best, Eusebio, Puskas and on and on. They were all generational talents capable of wonders. Most of them played at a World Cup. Some of them were at their finest there. But they didn't win. That is the final hurdle.
It's not fair – more often than not, the opportunity to do so is an accident of birth and timing. But it's also not negotiable.
Messi is 27 now. Young, but not young. In his prime, but not seeming so any more.
Two years ago, he was indisputably out alone in front, the best player in the world. You couldn't even have a decent bar argument about it.
Now he's back with the lead group, in amongst a half-dozen stars. There's something wrong with him. He could be drifting into the peloton faster than we fear.
Lately, he's begun vomiting during games. He's explained that away as nerves, and something he's always done. People within the game who've observed him for years don't recall it.
His own grandfather gave an ill-advised interview a few days ago in which he said: "He looks a little weak. He doesn't run like he used to." Who would know him better?
Whether we want to admit this to ourselves or not, Messi has begun the long slide.
He's been playing on Barcelona's first team since he was 16. In 2006, he was the youngest player ever to feature for Argentina at a World Cup.
He's been at this so long and at so high a level, he acquired an aura of timelessness. It's cracking.
He arrived in Brazil with the (undeserved) reputation as a player who fades in the colours of his country. He's been the difference here, but he has not yet been Messi. He isn't able to dominate teams over full games. That's more down to the men around him than anything he's done himself.
After four games, we can say with confidence that Argentina is amongst the poorer sides in the top echelons of international soccer. Shot through with stars, no doubt, but they add up to very little as a whole. What they are is grim and grasping.
Other teams want to win. Argentina needs to win. Not that locker room "We need to do this, guys" rah-rah nonsense. We're talking a need motivated by the spectre of doom.
Argentines have their pick between two things to think about right now – a failing economy and football. Once they lose here, it's no longer a choice.
That's done very little to motivate the squad. Man by man, position by position, they've been dismally average and are getting worse.
Their Round of 16 game Tuesday against Switzerland may have been the most unwatchable of the tournament. A dreary slog fought mostly at midfield, until both sides agreed to stop fighting at all.
The Argentine fans on hand – perhaps 25,000 of them – were bopping for most of the first 20 minutes. They suffered through the remaining 100 from their seats, stunned into silence. They know their football. And so they know they're rooting for a dog.
There is only one exception.
When you watch him off the ball, Messi is remarkably still, spending long minutes during a game walking slowly around the forward third with his head down, staring at his feet. He's beyond needing to look busy.
The equivalent might be getting the chance to observe Michelangelo paint the Sistine Chapel, then watching him prime the ceiling for a week.
But just as you're about to give up and leave, he begins to sketch an outstretched hand.
Messi did nothing for most of two hours against a rugged and unlovable Swiss team. Then came the main chance in the 118th minute.
A dispossession in midfield. A square ball that found him in open space. He broke into a northeasterly sprint. The man tracking him, Fabian Schar, had good position. Messi tugged him slightly off-line with pace. Schar sprawled. Messi went through him.
Now pulling six men sideways across the pitch like a boat dragging fish in a net, Messi broke the Swiss defence. It was, by his standards, a simple layoff to an onrushing Angel di Maria. That was it. 1-0.
That has been his pattern throughout here. Hardly commanding, often dull and somnambulant for long stretches, but incisive in a single, crucial instant.
What better definition is there of greatness?
He can still be the best ever – better than Pele, better than Maradona. For now, it remains three-man competition.
All he needs to do is what seems, from this vantage, impossible. He needs to win the World Cup by himself.
It's that, or nothing.
Cathal Kelly