Japan were favourites heading into the tournament to win a record-extending fifth title, while Son Heung-min's South Korea were touted as their chief challengers.
But after early results in the group stage in Qatar generally went as expected, there was a major upset when Iraq defeated a strangely muted Japan 2-1 on Friday.
Japan had also looked unconvincing in their opener, coming from behind to beat Vietnam 4-2. On Saturday, Tottenham and South Korea skipper Son put his country ahead from the penalty spot after nine minutes against Jordan, but an anticipated goal rush never materialised.
Instead it was Jordan - ranked 64 places lower than their opponents - who were leading 2-1 in stoppage time at the end of the game, only for the South Koreans to salvage a 2-2 draw via an own goal.
Japan and South Korea are still in a strong position to reach the knockout rounds - both only need draws against Indonesia and Malaysia respectively to progress. But both looked anything but champions in recent days and must wait at least a bit longer to join Australia, Iran, Iraq and hosts and holders Qatar in the last 16.
It would be harsh to accuse Jurgen Klinsmann or his South Korea side - who are attempting to win the title for the first time in 64 years - of complacency. On the eve of the tournament, the German, a World Cup winner as a player, said that "every game will be a nail-biter, every game will be difficult".
"Asian football has improved a lot, a lot, the quality has risen over the last 10 to 15 years dramatically," he added.
Of the four teams already into the knockout rounds with two wins from two, Qatar have arguably been the most impressive. They sacked former Real Madrid coach Carlos Queiroz just a month before the tournament and
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