Ali hit two in the first half and two more in the second to go top of the goalscorers' charts with five altogether, as the 2022 World Cup hosts safely reached the round of 16.
However, there was little excitement at any of Qatar's goals as a long-running Gulf blockade of the resource-rich state prevented any fans from attending the game in Al Ain.
The tiny attendance of roughly 300 in the 16,000-capacity venue was dominated by two small groups of North Korean fans who sporadically cheered and waved flags.
Ali had time to control Akram Afif's cross from the left and bury his shot on nine minutes, and he then clipped in Hasan Al-Haydos's ball from the right two minutes later.
With the North Korean fans providing the only noise in the stadium, the team from the communist country had a couple of moments at the other end.
But just before half-time, it was too easy for Qatar once again as Afif hoisted a hopeful ball to the far post and Boualem Khouki climbed above his marker to head it in.
- 'Real shame' -
Ali completed the Asian Cup's first hat-trick 10 minutes after half-time, when he coolly dinked the ball over goalkeeper Kim Myong Guk after Afif's slide-rule pass into the box.
Afif fed Sudanese-born Ali again to make it 5-0 before Abdelkarim Hassan, the 2018 Asian player of the year, made it six with a strong run and finish.
Qatar's big win, greeted by a smattering of clapping at the final whistle, also confirmed the Saudis' progression from Group E with both teams on a maximum six points after two games.
Germany's Mark Slonek, one of the small number of neutrals in the oval, all-seater ground, said it was a pity that more fans couldn't make it.
"It's like a lower-tier game in Germany, there's maybe 100 people here.
More staff (than fans). I was expecting more than 1,000." It was a far cry from the nearly 34,000 fans at the tournament's curtain-raiser in Abu Dhabi, while more than 76,000 attended the 2015 final in Sydney.
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