In the late morning, clusters of Saudi and Argentinian fans chanted on metro trains headed north to the 80,000-capacity and largest stadium at Lusail.
While they all expected to support their respective teams, no one across the world would have expected the end result of the FIFA World Cup Group C encounter.
Argentina coming off a 35-match winning streak lost to the Green Falcons, who were competing in their sixth World Cup but had never previously won an opening game.
The 35-year-old Messi scored a 10th-minute penalty in a dominant first-half display where he and Lautaro Martinez also had three goals disallowed for offside.
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.
"Wow. I have all the feelings right now. We beat Argentina, one of the great teams! Our guys played so well, everything went right inside the stadium today. It was amazing," said Saad, a Saudi who is here from Riyadh for two weeks and wore a green Saudi Falcons scarf around his neck.
"Our team fulfils our dreams!" and "Where is Messi? We beat him!", the green-clad Saudis chanted over and over in the Lusail Stadium, on their feet and greeting every clearance, including one headed off the goal line with a deafening roar.
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. In potentially a good omen for Messi and his teammates, they still made it to the final then.
The entire game was played in an extraordinary atmosphere at the Lusail Stadium, with Argentina's traditionally massive and raucous following matched by the thousands of Saudis who had come over the border to cheer on their team.
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 as the Argentinians trudged off downcast, their supporters shaking heads in silence.
Qatar's Emir Sheikh Tamim bin Hamad al-Thani, who attended the game, raised a Saudi flag. Here is how delirious Saudi fans celebrated..(Photographs....)
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