The little man they had all come to see took just 10 minutes to give them what they wanted. A little stuttering run-up, a nudge of his left foot and the first page of a potential Christmas fairytale had been written.
Or so we thought. That's the thing about fairytales. They are so called because they rarely come true and two hours after Lionel Messi had converted a penalty, he was stood near the halfway line, hands on his hips, barely able to comprehend what had happened.
And what had happened was a result that will be recalled and referenced in decades to come, how Saudi Arabia and their journeymen took down the squad that many believe are destined to contest the final in this very arena – the magnificent Lusail Stadium – on December 18.
An elated Salem Al-Dawsari performs a flip in celebration after scoring what proved to be Saudi Arabia's winning goal
His strike beat Argentina goalkeeper Emiliano Martinez and picked out the top corner as Saudi Arabia came back from behind
The shock result was far from what Lionel Messi and Argentina expected in the first game of his farewell World Cup
The Saudi Arabian players could scarcely believe what had happened after the final whistle blew on an historic victory
Saleh Al-Shehri was able to get ahead of Cristian Romero inside the Argentina box to slide home Saudi Arabia's equaliser
Al-Shehri knee slides and is joined by his team-mates after bringing Saudi Arabia back onto level terms just after half-time
Saudi Arabia, which is located just next door to Qatar, were well supported with thousands of fans travelling to the match
For context, Argentina 1 Saudi Arabia 2 will now get mentioned alongside United States 1 England 0 (1950), Spain 0 Northern Ireland 1 (1982) and France 0 Senegal 1 (2002) for scorelines that left you open-mouthed in disbelief.
It looked easy for them in those opening 10 minutes, with Messi having his first shot after less than 100 seconds (he should have scored) and converting from the penalty spot when VAR deemed that Leandro Paredes had been wrestled to the floor. A penny for Harry Maguire's thoughts on that one.
It was all going so well for Argentina when Lionel Messi slid home a 12th-minute penalty to hand them the early advantage
Messi sent the goalkeeper the wrong way after VAR had intervened to alert the referee to pushing and shoving in the box
But from there, it was a story of frustration for Argentina, who saw three goals chalked off for offside during the first-half
Lautaro Martinez rounded the keeper to slot home but then looked back in despair to see the raised linesman's flag
Argentina (4-2-3-1): Martinez; Molina, Romero (Lisandro Martinez 59), Otamendi, Tagliafico (Acuna 71); De Paul, Paredes (Fernandez 59); Di Maria, Messi (c), Papu Gomez (Alvarez 59); Lautaro Martinez
Substitutes not used: Armani (GK), Rulli (GK); Foyth, Montiel, Pezzella, Palacios, Correa, Almada, Rodriguez, Mac Allister, Dybala
Coach: Lionel Scaloni
Scorer: Messi (pen) 10
Saudi Arabia (4-4-1-1): Al-Owais; Abdulhamid, Tambakti, Al-Boleahi, Al-Shahrani (Al-Breik 90+9); Al-Shehri (Al-Ghannam 78), Kanno, Al-Malki, Al-Dawsari; Al-Faraj (c, Al Abed 45+4; (Al-Amri 89)); Al-Buraikan
Substitutes not used: Al-Rubaie (GK), Al-Aqidi (GK); Madu, Otayf, Al-Hassam, Al-Najei, Bahebri, Al-Oboud, N. AlDawsari
Coach: Herve Renard
Scorers: Al-Shehri 48; Al-Dawsari 53
Booked: Al-Malki, Al-Boleahi, Al-Dawsari, Abdulhamid, Al-Abed, Al-Owais
Referee: Slavko Vincic (Slovenia)
Saudi Arabia had no inclination to attack and didn't threaten to have a shot on target during the first half; the sole intention of head coach Herve Renard was to try and frustrate Argentina by playing a high-risk, high line defence to catch their vaunted opponents offside.
With the help of VAR and some fractionally mistimed runs, it worked as Messi and Lautaro Martinez (twice) had goals disallowed by the most slender of margins. The way the game flowed, it seemed inevitable that Argentina would spring the trap once and get the buffer they needed.
What followed in the second half was quite extraordinary. The Saudi fans created a tempest, roaring on their team and interspersing it all with chants of 'Ole, Ole, Ole, Ole!' – it all proved to be quite inspirational.
They levelled in the 49th minute when Saleh Al-Shehri, a 29-year-old forward for Al Hilal, took advantage of Tottenham's Christian Romero not reacting quickly enough and his shot, with a bobble, spun away from Emi Martinez's dive.
You could feel the power shift in an instant. All around there were green shirts hooting and hollering – screaming even – that their team had pegged back one of the favourites but, quickly, it was about to get so much better.
In what seemed like their next attack, again down Argentina's right, Al Dawsari, another Al Hilal player, shaped to go one way before cutting inside and unleashing the strike of his life, a shot that whizzed past Martinez, the Aston Villa goalkeeper, before he realised what had happened.
Some of the games so far have felt artificial – the opening one between Qatar and Ecuador in particular – but this was bedlam, wonderful bedlam, everything that football at a major tournament should be when different cultures and styles collide.
Messi thought he was going to level things up in the 56th minute when the goal opened up in front of him but, seemingly from nowhere, Hassan Al-Tambakti, an unheralded defender for Al Shabab, slid in to make a tackle as if his life depended on it, pilfering the ball perfectly.
Al-Tambakti leapt to his face, punching the air as if he had scored, and really the tackle was as good as a goal. Messi, meanwhile, rocked on his haunches and shook his head, unable to comprehend how the moment had gone.
It would get even more extraordinary. Shortly after, Nicolas Tagliafico found himself at the back post, three yards out, seemingly ready to turn the ball in. What he hadn't counted on was Muhammad Al Owais flying like Superman to turn his shot aside.
Saleh Al-Shehri is pumped up after equalising for Saudi Arabia with a well-taken goal minutes after the interval
Al-Dawsari, who is nicknamed 'The tornado', then put Saudi Arabia into an unexpected lead just a few minutes later
There then followed an heroic - and sometimes painful - rearguard action as Saudi Arabia weathered Argentine pressure - defender Yasser Al-Shahrani had to go off in injury time after colliding with keeper Mohammed Al-Owais
There were understandably wild celebrations at the final whistle as Saudi Arabia celebrated their most famous result ever
Lionel Messi is consoled by Mohamed Kanno following a defeat that wasn't in the script of his final World Cup appearance
You sensed here that this would be Saudi Arabia's day and the feeling intensified in the final 10 minutes when Messi struck a free-kick from 25 yards horribly over the bar – it was from the kind of range you have seen him find the top corner so gloriously, on so many occasions.
Deep into injury time, which seemed to last as long as a period of extra-time, Argentina had run out of ideas and, deservedly, Saudi Arabia had seen the job through, the roar at the final whistle one to match the one that will come from the tournament winners next month.
Will it be Argentina? You can never say never but, on this evidence, Messi is dreaming the impossible dream.