Northern Ireland have been relegated from Nations League B after Romania were awarded a 3-0 win over Norway for their cancelled match on Sunday.
Michal Duris struck an extra-time winner as Slovakia profited from the few chances they had to stun Northern Ireland.
Hungary, Iceland, Scotland, Northern Ireland, Serbia, Slovakia, North Macedonia, and Georgia all advanced to the Euro 2020 playoff finals.
Norway beat Northern Ireland 5-1 in their Nations League match on Monday with Borussia Dortmund striker Erling Haaland leading the charge.
Serge Gnabry scored a hat trick as qualified Germany came from a goal down to crush Northern Ireland 6-1 in their final Euro 2020 qualifier.
Netherlands booked their place at Euro 2020 with a 0-0 draw against Northern Ireland, whose hopes automatic qualification slipped away.
Memphis Depay scored twice and Luuk de Jong was also on target as the Netherlands came back with 10 minutes left to beat Northern Ireland.
Germany beat hosts Northern Ireland 2-0 on Monday to get their Euro 2020 qualification on track as they bounced back from a loss to Netherlands.
Austria forward Valentino Lazaro curled in a stoppage-time winner to give them a 2-1 win away to Northern Ireland.
Roma forward Edin Dzeko scored his 300th and 301st goals as Bosnia beat Northern Ireland 2-0 in their UEFA Nations League clash.
The Republic of Ireland will join England, Scotland, Wales and Northern Ireland in exploring a potential bid for the 2030 World Cup.
Haris Duljevic opened the scoring for the visitors before Elvis Saric took advantage of Craig Cathcart's poor header to double the advantage.
Northern Ireland midfielder Chris Brunt has announced his retirement from international football, the Irish Football Association said on Tuesday.
Two headed goals from corners and a strike from Joel Campbell gave Costa Rica a comfortable 3-0 win over Northern Ireland on Sunday
Paul Smyth needed just four minutes to deliver on Michael O'Neill's assertion that "the future starts today" with a late winner for Northern Ireland.
Northern Ireland boss Michael O'Neill has claimed the FA of Ireland targets Catholic players to switch allegiance and play for the Republic.
Northern Ireland boss Michael O'Neill has signed a four-year contract extension, after turning down the Scotland managerial offer.
The Republic of Ireland will meet neighbours Northern Ireland in a friendly match in November this year.
Michael O'Neill is set to continue as manager of Northern Ireland after turning down the Scotland job.