As far as warnings go, this one was loud and clear.
You arrive at the World Cup as defending champions, expecting to waltz into the knockout stages without breaking a sweat but a spirited Mexican side reminded Germany that their Russian expedition is going to be anything but that.
The 2014 champions started their opening game with some verve, weaving passes and pressing the Mexicans. But once the North Americans found their footing, they took the game to the Europeans. They used their pace to good effect and exploited Germany's lack of it. They came with a clear game plan and stuck to it: use the pace on the wings to break Germany's shape.
Winger Hirving Lozano and midfielder Miguel Layun used their pace and trickery and combined with Javier Hernandez to create openings. And sure enough it was that combination which brought them the goal, Hernandez laying it off for Lozano who cut inside and scored.
But the worry for Germany is not just the goal. Mexico might have had one or two more if they had been a little more decisive with the final ball. They pressed the Germans in numbers and countered as soon as they won the ball. There were many instances where Germany's lack of pace in the midfield area was exposed as they were outnumbered on the counter attack.
Midfielder Mesut Ozil endured a particularly torrid afternoon and his refusal to track back will be a worry for Germany. Toni Kroos ignored his usual passing game to attempt potshots from outside the box which was another bizarre strategy while Germany's prolific World Cup goal scorer Thomas Muller looked listless. All these things raise several questions for coach Joachim Low ahead of their upcoming group matches against Sweden and South Korea. Lots of decisions to be made.
But just one glance at the German squad will remind you that they have enough quality to beat any opposition. Apart from a strong starting lineup, they boast of a talented bench and also have enough experience within the ranks.
And for argument's sake, it should be noted that if there is one game you can lose and get away with at the World Cup finals, it is the opener. One might argue that it's safer to lose the third group game with qualification already secure but that breaks the winning momentum. Defeat in the opener meanwhile serves as a wake-up call.
All is not lost yet for Germany. It's still possible to turn this around and even finish the group as table toppers. But they will do well to remember that in three out of the last four World Cups, the holders (Spain in 2014, Italy in 2010 and France in 2002) crashed out in the group stages.
Germany really need to buck up if they want to avoid making it four out of the last five.
Elsewhere, Brazil were held to a 1-1 draw by Switzerland. The Selecao started strongly thanks to Coutinho’s first half curler into the top corner but they were listless after the break and could not find a second against the resilient Swiss.
There was an element of controversy in Steven Zuber’s equalizer as he looked to have shoved his marker before scoring off the corner. But the goal was given and Brazil struggled after that. All their star players went missing in the second half.
Like Germany, they too have some soul searching to do ahead of their upcoming games against Costa Rica and Serbia.
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