The midfielder claimed a sumptuous assist for Mikel Oyarzabal to make it 2-1 just before half-time, and played the full game as Spain won despite the home side equalising on three occasions.
Spain remain top of their European Under-21 Championships qualifying group, with Northern Ireland in second place.
Slovakia began their King's Cup campaign with a 2-1 victory over United Arab Emirates in Bangkok. Martin Dúbravka played the whole match in goal, and is likely to keep his place for Sunday's final against hosts Thailand.
UAE and Gabon will meet in the third-fourth play-off game.
Meanwhile, Islam Slimani played no part in Algeria's 4-1 victory over Tanzania.