INGLEWOOD, Calif. — The script almost wrote itself. Spain manager Luis de la Fuente’s decisions to leave Pedri out of the starting lineup and insert Mikel Merino as a late substitute might have raised eyebrows at the time, but they turned out to be masterstrokes of genius in the World Cup quarterfinal between Spain and Belgium on Friday. Pedri had started every match of Spain’s march through the tournament and had become one of the pillars of the midfield. In his place came Fabián Ruiz, who had only started Spain’s opener against Cape Verde. Spain’s Mikel Merino (6) celebrates scoring their second goal in front of Belgium’s Timothy Castagne (21) and goalkeeper Senne Lammens (12) during the World Cup quarterfinal soccer match between Spain and Belgium in Inglewood, Calif., near Los Angeles,