Reigning champions Italy lost their last group game but still claimed top spot, while La Rojita were Group B runners-up and remain unbeaten so far this summer.
Match preview
Despite losing 3-2 to Ukraine on Sunday, after fielding a much-changed side for their final Group A game, Italy are through to the knockout phase of another Under-19 Euros, having lifted the trophy as recently as last year.
With qualification already wrapped up following wins over Norway and hosts Northern Ireland, Bernardo Corradi rotated his squad at Inver Park, where the Azzurrini fought back from one goal down to lead 2-1 after 52 minutes.
Although strikes from Tommaso Ebone and Marco Romano put them within touching distance of a perfect group record, Italy then conceded twice more, with Christian Corradi receiving a second yellow card after conceding the penalty that produced Ukraine's winner.
Nonetheless, they remain on track to retain the title, having previously swept through qualifying unbeaten and lost just twice throughout 2024.
Sixteen-year-old AC Milan striker Francesco Camarda - who also played a part in the Under-17 squad's recent European Championship win - has scored twice to sit one behind Norway's Daniel Braut in the golden boot race, and head coach Corradi certainly has plenty of firepower at his disposal.
En route to Northern Ireland, Italy scored freely, and with a tally of 20 goals from their last seven matches, they may take some stopping in the semi-finals.
Before setting off on that spectacular scoring streak, the Azzurrini were beaten 3-0 by Spain in a January friendly, so they will be cautious about meeting their Iberian rivals again on Thursday.
Picking up a point on Monday ensured Spain's presence in the final four - and at next year's Under-20 World Cup finals in Chile - as they finished second in a competitive Group B.
Despite trailing to France with less than half an hour remaining, Jose Lana's side struck back through Dani Rodriguez in the 65th minute, before Simo Keddari headed home what appeared to be the winner. However, a late own goal from goalkeeper Raul Jimenez then denied La Rojita first place.
Having now progressed past the group stage in each of their last eight appearances, Spain - beaten semi-finalists last year - are intent on claiming a ninth Under-19 trophy this weekend.
Italy Under-19s European Under-19s Championship form:
W
W
L
Spain Under-19s European Under-19s Championship form:
Team News
Italy rested several players last weekend, but the likes of Milan trio Francesco Camarda, Davide Bartesaghi and Kevin Zeroli are all likely to return for Thursday's semi-final.
As Christian Corradi was sent off against Ukraine, Filippo Mane should come back into the champions' defence, with Renato Marin also resuming his role between the posts.
In addition to rising star Camarda, boss Bernardo Corradi has some tough calls to make in the final third: Simone Pafundi - who was the Azzurrini's top scorer in qualifying and set up two goals against Norway - Bologna's Tommaso Ebone and Lorenzo Anghele of Juventus are all in contention.
Meanwhile, Spain coach Jose Lana has had to do without new Chelsea signing Marc Guiu, who withdrew from the squad, but Ivan Bravo, Dani Rodriguez and David Mella should form an impressive attacking triumvirate.
Real Sociedad's Daniel Diaz and Real Betis winger Assane Diao are also in the mix, but it may be an unchanged team that starts in Belfast.
Italy Under-19s possible starting lineup:
Marin; Magni, Chiarodia, Mane, Bartesaghi; Mannini, Lipani, Ciammaglichella; Zeroli; Pafundi, Camarda
Spain Under-19s possible starting lineup:
Jimenez; David, Keddari, Gasiorowski, Munoz; Hernandez, Andres, Belaid; Rodriguez, Bravo, Mella