Northern Ireland fell to their second consecutive defeat in their World Cup qualifiers but their place in the play-offs, where they will be unseeded, was confirmed after Scotland drew with Slovenia.

Only eight of the nine group runners-up will make it through to next month’s play-offs and confirmation of their play-off berth arrived less than an hour before Michael O’Neill’s side played their final group game.

Chris Brunt’s own goal from under his crossbar, in the 71st minute, was enough to give Norway victory. Lars Lagerback’s side were already out of contention for second place. Norway have not qualified for the finals of a tournament since Euro 2000.

Northern Ireland had guaranteed second spot last month with a 2-0 victory over Czech Republic but, with results against the bottom-placed sides in each group discounted in the race for the playoffs, their situation was still not resolved heading into this international break.

They began the day knowing anything other than a Scotland victory would see them make it through regardless of how they fared at the Ullevaal Stadion. Scotland drew 2-2 in Ljubljana.

The draw for the play-offs takes place on 17 October and it will be seeded, meaning Northern Ireland’s defeat against Norway is still important if they are to avoid Portugal – the reigning European champions – Italy and Wales, who were semi-finalists at Euro 2016.

The visitors looked largely untroubled but would have been scaring none of the other play-off-bound teams on this evidence either as a potential counterattack was snuffed out by Havard Nordtveit.

O’Neill called for Kyle Lafferty from the bench with 21 minutes remaining yet Northern Ireland fell behind moments later in bizarre fashion.

With Conor McLaughlin down on the ground injured, Stefan Johansen’s cross from the left was pushed into the air by a backpedalling Michael McGovern and Brunt’s attempted clearance with the outside of his boot was somehow lashed into the roof of his own net.

At half-time O’Neill took off Oliver Norwood, replacing him with George Saville. A few weeks ago his Northern Irish eligibility was not even known but Saville is expected to be a key figure for O’Neill and almost made an instant impact when he won the ball, fed Conor Washington and nearly finished off the move before losing his balance as Birger Meling came across.

Brunt’s error stirred O’Neill’s side into life for the first time all evening and they came close to levelling straight away. Stuart Dallas’s terrific volley from the edge of the box was helped wide by Orjan Nyland’s fingertips while Lafferty, with a header over, and Conor McLaughlin, with a poked shot at the Norwegian keeper, came close too.

O’Neill made sure Corry Evans will be suspension-free next month when taking him off, although they will face a difficult task to reach the World Cup for the first time since 1986, with Cristiano Ronaldo possibly waiting for them next month. Guardian sport