Iran's coach said he was "angry" at his players' wastefulness after they toiled to a 1-0 win over Hong Kong on Friday to reach the knockout rounds of the Asian Cup.

On paper this fixture was among the biggest mismatches at the tournament in Qatar, with Iran ranked 21 in the world and Hong Kong 150.

Iran are also among the favourites and chasing a record-equalling fourth continental crown, but for all their possession, they had only one goal to show for it.

Mehdi Ghayedi slid a shot across the six-yard box and past the despairing grasp of goalkeeper Yapp Hung-fai in the 24th minute, the ball nestling in the bottom-right corner.

While happy to have reached the last 16 with a group game to spare, coach Amir Ghalenoei was "angry about the opportunities that we lost in this game".

It was actually Hong Kong -- playing at their first Asian Cup in more than 55 years -- who had opportunities early on, especially when Brazil-born forward Everton Camargo blazed over the bar from inside the box.

The missed chances continued to pile up for the team from southern China, who occasionally had Iran rattled in front of 36,412 at the Khalifa International Stadium.

Philip Chan, who scored in the very same net during Hong Kong's 3-1 loss to United Arab Emirates, sliced a gilt-edged opportunity after some haphazard Iran defending.

Yapp saved well from a Shahriyar Moghanloo header, before referee Hanna Hattab brought an end to an unexpectedly even first half.

After watching his side fail to lay a glove on Iran after the restart, Hong Kong coach Jorn Andersen made an attacking triple substitution, sending on forwards Stefan Pereira and Michael Udebuluzor along with midfielder Wong Wai.

But the score remained unchanged, Ramin Rezaeian and Karim Ansarifard both missing chances to extend Iran's lead.

Rezaeian said after the match that "I myself could've scored three goals" as he also lamented his team's missed chances.

Despite successive defeats, Andersen was pleased his team could go toe-to-toe with one of Asian football's giants.

"We played two games where we didn't see the difference between the two teams," he said.

"We pushed them, attacked them, pressed them and a team like Iran did not know how to play football against us."

Next up for Hong Kong are 99th-ranked Palestine on Tuesday, and in a tournament where the four best third-placed teams also progress, both are still alive.