Son Heung-min's stuttering South Korea play Saudi Arabia while Palestine face hosts and holders Qatar as the Asian Cup kicks into high gear with the knockout rounds from Sunday.

The tournament has been whittled down from 24 teams to 16 but trying to predict who lifts the trophy on February 10 looks more difficult than ever.

Japan came to Qatar as favourites and looking to win the title for a record-extending fifth time, but they reached the knockout phase as only runners-up in their group behind Iraq.

Iraq impressed in deservedly beating Japan 2-1 and along with Iran and Qatar were the only teams to win all three games in the first round. Iraq play Jordan and Iran meet Syria next.

Jurgen Klinsmann's South Korea would have faced Japan had they topped their group, but they were held 3-3 by Malaysia in their final game and play Roberto Mancini's Saudis on Tuesday.

South Korea, who are trying to win the Asian Cup for the first time in 64 years, also drew with Jordan and coach Klinsmann is anticipating "a battle".

"You cannot underestimate any team -- every team is tactically very smart, they can hurt you even if you have 85 percent possession," the German legend warned.

"There is no easy team in Asia to play," he added.

Skipper and talisman Son has scored twice at the tournament, both penalties, and called their madcap stalemate with already eliminated Malaysia "a big wake-up call".

Opponents Saudi Arabia topped their group with two wins and a draw, but they have not really fired in attack and made hard work of defeating nine-man Kyrgyzstan 2-0.

"We know it will be a very difficult match, not only for us, but also for them," said Mancini of the looming South Korea clash, which is undoubtedly the game of the last 16.

In other matches, Japan play Bahrain, but like the Koreans, they have not lived up to big expectations so far.

Brighton winger Kaoru Mitoma is yet to play a single minute and coach Hajime Moriyasu has refused to put a timeframe on his return from injury.

"I don't want to use him until he's ready," said Moriyasu, admitting he had taken "a risk" in bringing him to the tournament.

The coach looks set to stick with inexperienced goalkeeper Zion Suzuki despite the 21-year-old being culpable for at least two of the five goals Japan conceded in the group stage.

Reigning champions Qatar impressed in tearing through Group A and face Palestine, who defeated Hong Kong 3-0 -- their first victory in the history of the competition.

That landmark achievement, against the backdrop of the war in Gaza, also put the Palestinians into the Asian Cup knockout rounds for the first time.

The hosts will be strong favourites to reach the last eight and with home advantage look a good bet to go deep in the competition.

But no matter what happens on Monday, the inspirational Palestinian captain Musab Al-Battat said his team had fulfilled "a promise to the Palestinian people".

"We managed to put a smile on the faces of those who follow us... inside or outside Palestine," he said.

The knockout phase begins on Sunday when Australia play Indonesia, followed the same day by the United Arab Emirates against tournament debutants Tajikistan.

At 146 in the world, Indonesia are the lowest-ranked team left in the tournament and squeezed through with one win and two defeats from their three group games.