Finland's triumph in Belfast dealt an early blow to Northern Ireland's aspirations of qualifying for Euro 2024, leaving them to regret squandered opportunities and a goal that was incorrectly declared as the goal.
Ben Kallman's tying goal in the first half gave the guests their first Group H points.
Just after Josh Magennis, the substitute had blasted over, VAR disallowed Dion Charle's close-range attempt for handball
NI won their first game 2-0 vs San Marino.
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The team has been feeling more upbeat since Michael O'Neill was chosen to serve as manager again because of the victory in San Marino.
They had a positive attitude going into his first game back at Windsor Park.
Although the hosts put on a performance that sometimes seemed disjointed and relied on the soaring running power of teenager Conor Bradley to generate an offensive threat, the 17,900-strong home fans gave the team and management terrific vociferous support throughout the game.
The team's failure to score goals has long been an issue, even during some of O'Neill's successful first term, and it cost them against a group opponent that fell 3-1 to top-seeded Denmark on Thursday.
The Danes were unexpectedly defeated by Kazakhstan earlier on Sunday, and Slovenia now leads the group after defeating San Marino, the team with the lowest world ranking.
Finland's first goal came from a right-sided attack in which Robin Lod expertly manoeuvred Jamal Lewis and Jordan Thompson before sending in a low cross that Teemu Pukki of Norwich City received.
Kallman intercepted his missed shot at the back post, and the visitor poked the ball past Bailey Peacock-Farrell in front of The Kop to take the lead just as the hosts were having their best stretch of the game.
In minute 63, Charles scored a close-range goal after a corner fell to him, giving Northern Ireland hope that they had equalized.
But after a VAR review, referee Ivan Kruzliak determined that the player had been controlling. He used his hand, not his chest, to catch the ball.
In the first minute, a Thompson pull-back from the byeline landed just behind Conor Washington, who was poised to pounce yards from goal. It was Northern Ireland's first significant chance at the game.
The players nearly gave the Kop the desired answer when Dion Charles was on the end of a nice move and came agonizingly close to tying the score just before halftime. The Kop had already started supporting their team after they conceded.
Shea's play has become more refined. The striker for Bolton's turn-around shot was well smothered by the goalkeeper and captain Lukas Hradecky, who might have been more troubled if Charles had gotten some elevation on his effort. He released Bradley on the right, and Charles observed him advance purposefully before finding Charles with a perfectly-weighted pass.
Early in the second half, O'Neill made the risky decision of bringing in Magennis from the bench instead of injured centre-back Daniel Ballard. Northern Ireland's formation was changed from 3-5-2 to 4-3-3, with Washing and Dion Charles forming a front three on either side of Magennis.
Following Bradley's goal-bound header from a left-wing cross, Magennis had a great chance to score just minutes after entering the game, but he missed the crossbar.
As the game continued, Northern Ireland started to appear ragged, and the substitutes George Saville and Gavin Whyte could not have the impact O'Neill had hoped for. The disallowed goal in minute 63 was the closest they came to tying the score.
With a loss, Northern Ireland drops to fifth place in Group H, one of four teams with three points after the first two rounds of games, ahead of a doubleheader in June against Kazakhstan at home and on the road against Denmark.