If the World Cup needed a shock to kick into gear, Saudi Arabia delivered against one of the pre-tournament favourites Argentina with one of the greatest surprises in history.
Lionel Scaloni's side were stunned in the second half of their Group C opener as Saudi Arabia became the first non-European side to beat La Albiceleste in the competition since Cameroon in 1990.
Elsewhere in Group C, Robert Lewandowski's wait for a World Cup goal went on after being denied from the penalty spot in a goalless draw between Poland and Mexico.
Denmark failed to breach the Tunisia defence in another stalemate on Tuesday in Group D, while Australia threatened another unlikely victory before defending champions France responded in style.
Here, Stats Perform looks at the key data from a memorable day of international action.
Argentina 1-2 Saudi Arabia: Messi record in vain as Renard's men make history
Lionel Messi became just the fifth player to score at four different World Cups but that mattered for little as Saudi Arabia fought back for a record-breaking 2-1 win over Argentina.
Messi joined an illustrious list alongside Pele, Uwe Seeler, Miroslav Klose and Cristiano Ronaldo with a first-half opening penalty, while scoring in five consecutive international games for just a second time.
Saleh Al Shehri levelled before the emphatic winner from Salem Al Dawsari, who became only the third Saudi Arabian to score more than one World Cup goal and just the second to score at two different editions.
The second-half shock saw Argentina, whose 36-match unbeaten run in all competitions ended, lose a match at FIFA's top tournament after opening the scoring for the first time since 1958 against Germany.
It was also the first time La Albiceleste lost when leading at half-time since the 1930 final against Uruguay, while Saudi Arabia are the first Asian side to defeat Argentina in the competition at the fifth attempt.
The omens – albeit unlikely – are good for Saudi Arabia given the last three sides to beat La Albiceleste have gone on to make the final, with Germany (2014) and France (2018) winning the tournament.
Denmark 0-0 Tunisia: Danes held but Eriksen shines on return
Christian Eriksen returned to major international football just 18 months after suffering a cardiac arrest at the delayed Euro 2020, though his best efforts could not to help Denmark past Tunisia in a 0-0 draw.
Midfielder Eriksen created his most chances in a World Cup match (five), only Denmark's Michael Laudrup has provided more for his country in a single match at the tournament (six versus Nigeria in 1998).
But Eriksen, who became the first Danish player to feature in the competition in his teens, twenties and thirties, was helpless to stop Tunisia from keeping just their second clean sheet in 16 World Cup outings.
That was not for a lack of trying, though, with 24 shots attempted – the most efforts without finding the net in a goalless World Cup game since Netherlands versus Costa Rica in July 2014 (26 shots).
Denmark, who saw a late penalty appeal dismissed, dropped early ground in Group D after becoming just the third side to draw four consecutive World Cup matches, also Belgium (five from 1998-2002) and Republic of Ireland (four in 1990).
Mexico 0-0 Poland: Penalty hoodoo haunts Lewandowski
Poland star Lewandowski remains in search of his first World Cup goal after seeing his second-half spot-kick saved by Guillermo Ochoa in a 0-0 draw with Mexico.
Such struggles at the World Cup are no surprise for Poland, who are the first team to not score three consecutive penalties since such records began in 1966 – Kazimierz Deyna (1978) and Maciej Zurawski (2002) the others to miss.
Ochoa guessed the right way to deny Lewandowski low down to his left as the Mexico goalkeeper, aged 37 years and 132 days, became the second-oldest player to save a World Cup spot-kick.
Only Belgium's Thibaut Courtois (39) has made more saves than Ochoa (37) since the 2014 edition as the 37-year-old continues to deliver on the world's biggest stage for his country.
Poland must be wondering what they have to do to score in a World Cup opener, having gone winless in seven such games since 1978 (D4 L3) and netting just once in those matches.
France 4-1 Australia: Giroud matches Henry record as champions start in style
Olivier Giroud joined Thierry Henry as France's top scorer in history with a brace as Les Bleus avoided previous failings of defending champions after a 4-1 win over Australia.
Didier Deschamps' side are the first reigning champion to win their opening game since Brazil in 2006 after recording the largest victory in a current World Cup holder's first match of their title defence.
It was not all straightforward, though, as Craig Goodwin opened the scoring with Australia's earliest goal in the tournament's history – timed at eight minutes and 23 seconds.
Les Bleus bounced back to the first time they had conceded the opener at a World Cup since the 2014 quarter-final against Germany as Adrien Rabiot headed home.
Rabiot then became France's first tournament debutant since Christophe Dugarry in 1998 to score and assist by teeing up Kylian Mbappe, who is the youngest player to score five Les Bleus goals in the world finals – aged 23 years and 337 days.
Giroud stole the headlines, however, as he matched Henry's 51-goal mark after becoming the second-oldest player (36y 53d) to score a World Cup brace, only behind 38-year-old Roger Milla for Cameroon in 1990.