Unheralded Saudi Arabia have pulled off one of the biggest shocks in World Cup history with a 2-1 win over Lionel Messi's Argentina thanks to a scintillating second-half comeback.
On his fifth and perhaps last quest for the only major trophy to elude him, the 35-year-old Messi scored a 10th minute penalty in a dominant first-half display on Tuesday in which he and Lautaro Martinez also had three goals disallowed for offside.
But Saudi Arabia, the second-lowest ranked team in the tournament after Ghana, threw caution to the wind at the start of the second half, charging at Argentina's defence in front of a frenzied 88,012 crowd.
Saleh Al-Shehri squeezed in a low shot in the 48th minute while Salem Al-Dawsari curled in a scorching strike from the edge of the penalty area in the 53rd to leave Argentina and Messi looking utterly shell-shocked in the group C opener.
Despite plenty of possession after that, Argentina were unable to penetrate Saudi Arabia, who were competing in their sixth World Cup but had never previously won an opening game.
The game was played in an extraordinary atmosphere at the Lusail Stadium, with Argentina's traditionally massive, raucous following matched by thousands of Saudis.
"Our team fulfils our dreams!" and "Where is Messi? We beat him!", the green-clad Saudis chanted over and over, on their feet and greeting every clearance with a deafening roar.
Both teams have Mexico and Poland to come, with Argentina needing an immediate reaction if Messi is to match Diego Maradona's immortal status in his homeland by bringing home the World Cup.
The result revived old question marks over Argentina's defence and broke their amazing 36-match undefeated run - one short of the international record of 37 games unbeaten held by Italy.
It also marred Messi's achievement of becoming the first Argentinian to score in four World Cups on his 20th appearance in the tournament.
Only Maradona has played more games for Argentina at the World Cup, 21 in all.
"This hurts a lot. We were dreaming of starting the World Cup with a win," said Messi's strike partner Martinez. "But it's happened and now we have to train and think forward.
"We lost this game because of our own mistakes, most of all in the second half. There are details that make a difference and we need to correct our mistakes."
It had all looked so different at the start when the marauding Messi nearly scored in the opening seconds, celebrated joyfully after sending Saudi goalkeeper Mohammed Al-Owais the wrong way with his penalty, then had another goal disallowed.
The Saudis' feat was all the more remarkable given the departure of their influential captain and midfielder Salman Al Faraj just after halftime, clutching a hamstring.
Argentina's last defeat was by Brazil in the semi-finals of the Copa America in July 2019. They are ranked third, 48 places above Saudi Arabia, by world football's governing body FIFA.
Argentina's last defeat in their opening match at a World Cup was against Cameroon in 1990 - but they went on to reach the final.
The Saudis could hardly contain themselves after their giant-killing act, falling to the floor in prayers and tears before running to celebrate with their fans.
Midfielder Abdulelah Al-Malki said they'd been fired up like never before by their coach Herve Renard.
"Renard made us cry with the motivation before the match and stoked us up during halftime," he said, affectionately calling the Frenchman "crazy".