Defending champions Germany made a disastrous start to their bid to win back-to-back World Cups with a shock defeat by Mexico.
Hirving Lozano's first-half goal was the difference between the two sides in an enthralling encounter in Moscow, but the surprising result was not the only concern for Germany coach Joachim Low.
His disjointed side looked extraordinarily vulnerable on the break even before Javier Hernandez punished them with the pass that set up Lozano to cut inside and fire home.
Toni Kroos almost replied instantly with a free-kick but Guillermo Ochoa tipped it on to the bar and that was the closest Germany came to an equaliser.
Despite facing some sustained late pressure, Mexico held on to inflict a first World Cup defeat on Die Mannschaft since they lost to Spain in the 2010 semi-final.
This was also the first time a German side had lost their opening game of this tournament since 1982, when West Germany were upset by Algeria.
It could turn out to be a damaging defeat too. Although Germany will still be expected to beat Sweden and South Korea and progress, the runner-up in Group F will face a last-16 tie against the Group E winner, expected to be Brazil.
Unconvincing Germany pay the price
Low's side had come into the tournament on the back of some unconvincing displays and results in their recent friendlies, but there had been no sign of panic in their camp.
Things were very different at a noisy Luzhniki Stadium, with Germany showing little of the composure or class we associate with them at major finals.
Even before they went behind, they were often over-run in midfield, with Kroos and Sami Khedira unable to offer their defence any protection from Mexico's rapid counter-attacks.
Germany's right flank seemed susceptible on the break, with Joshua Kimmich's forays forward leaving space for Lozano and Hernandez to gallop into unchallenged.
If 'El Tri' had made more of their chances, or found a better final ball, then they could have been two or three goals ahead by half-time.
At the other end, Germany were also unconvincing in the early stages, with their famed midfield machine struggling to find a way through Mexico's determined defence.
Although they improved in the second half, and dominated possession, Germany's finishing touch eluded them and Mexico continued to cause problems on the counter.
Germany's sheer desperation to equalise was evident by the number of men they threw forward late on, including, at one stage, goalkeeper Manuel Neuer.
It left them even more exposed in midfield and at the back in the closing stages, and Mexico might have punished them further. In the end, though, one goal was enough.
Mexico defence holds off German fightback
Mexico had only won one of their past 11 meetings with Germany and their most recent ended in a 4-1 defeat by what was virtually Low's B team at last year's Confederations Cup.
But they fully deserved this victory, which brought huge celebrations from their thousands of fans who had travelled to Moscow, many in typically colourful costumes.
The intensity of Mexico's play was matched by their supporters, who not only out-numbered their Germany counterparts, but also out-sung them. That was not the only reason Germany looked rattled, but it certainly helped.
Lozano's pace and willing to drive at Germany's defence was the highlight of the first half, with only a last-ditch Jerome Boateng block denying him in the first minute and setting the pattern for the early stages.
The second half was more of a demonstration of Mexico's defensive capabilities, especially near the end - but they survived.
Mexico arrived in Russia with the hope of finally managing a 'quinto partido' or fifth match, after losing in the last 16 at the past six World Cups.
Juan Carlos Osorio's side have a lot more work to do before they achieve that aim, but his famed attention to detail paid off here and they appear strong both technically and tactically. They will be tough to beat.
Man of the match - Hirving Lozano (Mexico)
'Everybody is unhappy and crestfallen' - what they said
Mexico coach Juan Carlos Osorio: "In the first half, we were the better team. In the second half, they tried to attack more. We prepared yesterday for their use of Mario Gomez up front. We practised defending with four midfielders and three players up front and that is almost how we got the second goal.
"We showed we have a bright future and I am very satisfied with what we did. We played with bravery when it was needed and also defended with all of our hearts."
Germany coach Joachim Low: "In the first half, we played very badly. We were not able to impose our usual way of playing, attacking, and there were lots of counter-attacks against us and we were very vulnerable.
"In the second half, we were able to press more, but Mexico drew back and then carried the ball forward fast. We had a couple of shouts, but it seemed jinxed and the ball did not go into the goal. Everybody is really unhappy and crestfallen but we have to put this behind us. Our team has experience of losses."
Lozano carries form into finals - the stats
■ Mexico have won their opening match at a World Cup for the fifth time in their past six tournaments (drawing the other).
■ This is the third consecutive World Cup in which the reigning champions have failed to win their opening match - Italy drew 1-1 with Paraguay in 2010, and Spain lost 5-1 against the Netherlands in 2014.
■ Mexico beat Germany for only the second time - their last win against them came in a friendly in June 1985.
■ Hirving Lozano was Mexico's top scorer in 2018 World Cup qualifying (four goals) and scored his first finals goal in this match.
■ Germany had 26 shots, the most by a side without scoring in a World Cup match since 2006 (Portugal v England, 29 shots in a 0-0 draw).
■ Mexico have lost just two of their past 18 World Cup group games (W9 D7).
■ This was Germany's first defeat in a competitive match since losing 2-0 to France in the Euro 2016 semi-final.
■ Germany named their oldest starting XI for a World Cup match (average age: 27 years 310 days) since the 2002 final against Brazil (28 years 166 days).
■ Rafael Marquez featured in his fifth World Cup finals (2002, 2006, 2010, 2014 and 2018), becoming just the third player to achieve this feat - along with Mexico's Antonio Carbajal (1950, 1954, 1958, 1962 and 1966) and Germany's Lothar Matthaus (1982, 1986, 1990, 1994 and 1998).
What next?
Mexico play South Korea on Saturday in Rostov-on-Don (16:00 BST), while Germany take on Sweden in Sochi later the same day (19:00).
BBC
