His Iraq team have scored a penalty 17 minutes into added time to claim a dramatic 2-1 home win over the United Arab Emirates and secure a 3-2 aggregate playoff victory that keeps the country's 2026 World Cup qualification dream alive.
Amir Al-Ammari struck from the spot on Tuesday night to take the Australian coach's side into March's intercontinental playoffs in front of a packed-out Basra International Stadium.
The winner came after substitute Mohanad Ali had headed in a 66th-minute equaliser for the hosts, who had gone behind to Caio Lucas' opener 14 minutes earlier.
Iraq, who are trying to qualify for the World Cup for the first time since their debut in 1986, will now join five other teams in the playoffs, with two spots at the finals in the United States, Canada and Mexico available.
Under Arnold, the Socceroos had their most successful World Cup campaign in Qatar in 2022, only narrowly bowing out to eventual winners Argentina in the round of 16.
Iraq were second-best for much of the game but a set piece allowed Arnold's side to pull level.
Al-Ammari swung his free kick from the left flank towards the six-yard box and Ali's header took a deflection off Nader that ensured goalkeeper Khalid Eisa had little chance of preventing the ball from crossing the line.
Ali was heavily involved again as Iraq were awarded the decisive penalty, the striker connecting with a header that Nader swatted away with his arm and referee Yusuke Araki pointed to the spot after viewing the pitchside monitor.
Al-Ammari thumped the spot kick high into the goal as Eisa dived the wrong way to spark wild celebrations in the stands.
"Thank God we won," Iraqi fan Ahmed Buthan said as he was celebrating with his three children at the stadium.
"We will continue the road to World Cup, I am positive."
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