Saudi Arabia produced one of the biggest upsets in World Cup history by toppling Argentina, who cannot afford another slip-up if they are to reach the knockout stages.
Argentina fans back home were up with the lark for a 7am kick off, only to watch their team deliver a desperately poor showing that shattered a 36-game unbeaten run.
This is Lionel Messi's last chance to win the World Cup and expectations were high after winning last year's Copa America. They now face two nervy encounters against Mexico and Poland as they try to avoid a humiliating group stage exit.
Graeme Souness and Roy Keane were working as pundits for ITV and agreed that Lionel Scaloni's side had fallen short in all departments against a surprisingly bold Saudi Arabia. Former Liverpool midfielder Souness claimed Argentina lacked the aggression and fight typically associated with their style of play.
Souness, visibly shocked, said: "In my time in football when I've played against Argentinians I never ever got an easy encounter - that was a shadow of any Argentinian side I've ever seen, they were a shadow today."
Keane told viewers: "They weren't as a team today - it's a huge setback for them, huge."
Joe Cole, Telegraph Sport columnist, added: "Argentina came into this expecting to win, thirty six games unbeaten. This is a huge test now. Lionel Scaloni's got to lift that group of players and find a way of getting them back to what we expect - aggressive, quality - it's a huge ask for him."
It was a landmark day for Saudi Arabia's coach Herve Renard, who was sacked by Cambridge United earlier in his career. Saudi had only won one match at the World Cup before Tuesday, but their aggressive pressing and physicality disrupted Argentina's rhythm. Saleh Al Shehri and Salem Al Dawsari were the goalscoring heroes with two excellent finishes.
"We prepared very well and today all the stars in the sky were in the same line for us," Renard said.
"They have amazing players, but this is football. Sometimes things completely crazy can happen."
The Frenchman added: "It's also happened to us sometimes when we play a lower team. This is sometimes what the people do not understand.
"Do you imagine Lionel Messi (is highly motivated) against Saudi Arabia? Of course he will say 'we need to start very well' but you know motivation is not like they play Brazil. This is normal, this is part of football.
"We made history for Saudi football. It will stay forever. This is the most important thing, but we also need to think about looking forward because we still have very difficult two games."
Speaking to Argentine media after the game, Messi said: "It's a situation that this group of players has never been through, it's been a while since we suffered such a tough blow, we didn't expect to start like this,
"In five minutes of mistakes that we made, we went 2-1 down and then it was really tough and we lost organization and started punting the ball," he added in comments broadcast by Todo Noticias.
There was recrimination in the Argentine press, with Cristian Grosso writing for La Nacion that the team "became a ghost" after Saudi Arabia's opening goal and that Scaloni made selection mistakes.
La Nacion also point out that slip-ups at the start of a tournament are something of a theme with Argentina, who were beaten by Belgium in 1982 and Cameroon in 1990. They also drew 1-1 with Iceland in their first group game in Russia four years ago.
Mariano Dayan, writing for website Olé, called on Argentina to put the result behind them but said they 'emotionally short-circuited' once they found themselves in the unusual position of losing.
Olé's player ratings made for grim reading for Cristian Romero, who was awarded a 3/10 for what was described as his worst performance for the national team. The Tottenham defender was struggling with a groin injury before the tournament and looked sluggish on Saudi Arabia's opening goal.
Unsurprisingly, Saudi's famous victory led Arab News throughout the day on Tuesday, with more than 10,000 fans crossing the border to Qatar to roar on their team.
In their match report, Arab News say: "Playing a risky high defensive line, the athletic Saudis rode their luck in the first half when three times Argentina had the ball in the net only to be denied by an offside call.
"But in a chaotic start to the second half, the Saudis swarmed all over Lionel Scaloni's team and scored twice as the Arab nation beat the South Americans for the first time in five attempts."