Iraq winger Kerrar Jasim converted a rebound mid-way through the first half at the Al Rayyan Stadium in Doha and his goal was enough to set up a clash with Group D winners Australia.
Arash Afshin and Mohammad Nori were Iran's goalscorers, with Walid Abbas also putting through his own goal as Afshin Ghotbi's team completed the group phase as the only side with a 100 percent record.
Afshin was later sent off, however, and UAE defender Khalid Sebil also saw red to leave both sides with 10 men on the pitch at the final whistle.
Iran will now meet in-form South Korea -- for the fifth consecutive time at this stage of the tournament -- having already secured top spot in Group C thanks to a superior head-to-head record against Iraq.
Iraq dominated the first half against North Korea, with Iraqi striker Mustafa Kareem diverting Samal Saeed's downward header against the crossbar in the 17th minute.
The 2007 champions made the breakthrough five minutes later.
Kareem sent in a powerful, swerving shot from 22 yards that North Korea goalkeeper Ri Myong-Guk could only parry and Jasim slid in to score.
Kareem volleyed narrowly over from close range in the 37th minute, with a 35-yard free-kick by Jong Tae-Se that Mohammad Kassid saved comfortably the best that North Korea could offer in the first half.
Jasim was narrowly off-target with a long-range strike early in the second period, while Bochum striker Jong squandered a clear sight of goal when he swivelled and shot straight at Kassid with 13 minutes remaining.
Having already qualified, Iran made no less than nine changes to their line-up at the Qatar Sports Club Stadium.
The changes allowed UAE to take the initiative and Ahmad Khalil struck the left-hand post from a tight angle on 15 minutes after shuffling into the area from wide on the left.
The game became bogged down in midfield in the second half but in a rare moment of class, UAE goalkeeper Majed Nasser sprang to his right superbly to tip Ghasem Hadadifar's goal-bound effort around the post.
Iran broke the deadlock in the 70th minute, Afshin scoring from close range after striker Mohammad Gholami had hit the bar twice in quick succession with a pair of headers.
Afshin was shown a second yellow card for a reckless challenge on Nasser, with Sebil swiftly following him down the tunnel after a late foul on Hadadifar that earned him a second caution.
Nori applied the finish to a sweeping Iran move before Abbas's injury-time own goal -- his second in consecutive games -- killed the game off, as UAE, like North Korea, limped out of the tournament without a goal to their name.
The quarter-finals get under way on Friday, with hosts Qatar tackling three-time champions Japan and Group A winners Uzbekistan taking on Jordan.