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.
'No insecurities'
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 replaced him with Spaniard Tintin Marquez.
It is early days but the gamble has paid off so far, the reigning champions easing past Lebanon 3-0 to open the tournament and sealing their place in the next round with a 1-0 win over debutants Tajikistan.
In forward Akram Afif they have the joint leading scorer in the tournament, on three goals along with Iraq's Aymen Hussein, who scored both goals against a rattled Japan.
Coach Aleksandar Jankovic, whose China side were held 0-0 by Tajikistan and Lebanon, noted on Sunday "how balanced the tournament is".
"The distance is becoming shorter and shorter between the teams," he said on the eve of China's clash with Qatar, with his side's last-16 hopes in the balance.
Iran, the second-highest-ranked team in the competition after Japan, have already reached the knockouts as they chase a fourth Asian crown.
They thumped Palestine 4-1 but then laboured to a 1-0 win over Hong Kong, the lowest-ranked team in Qatar.
Graham Arnold's Australia were similarly unimpressive in going through with a stodgy 1-0 win over Syria - the winning goal was the Socceroos' only shot on target all game.
Jordan's coach Hussein Ammouta was disappointed to see a famous victory over South Korea snatched away but said it was proof there was little difference between the supposed big and small teams.
"What is certain is that every national team has to believe in their capabilities and should not go into any game with insecurities," he said.
