Goalkeeper Svetoslav Vutsov was one of eight changes from Bulgaria’s 6-1 loss to Turkey in Aleksandar Dimitrov’s disastrous first match in charge, and he dealt with the first threat to his goal – an Álex Baena strike after nine minutes.
Spanish dominance meant Vutsov’s teammates were forced to sit very deep, and they stood firm until Pedri slipped a pass through to Samu Aghehowa, who forced a top-drawer stop from Vutsov, before Pedri danced through himself, chipped the goalkeeper, and saw his effort come back off the crossbar.
Aghehowa’s attempts to score on his first international start continued to be thwarted when a quick turn and hit was palmed away by Vutsov, then on the half-hour mark, Pedri’s half-volley dragged wide took Spain’s total efforts to 15.
Mikel Oyarzabal added to that with a fearsome effort that flew just over, before Bulgarian resistance was finally broken 10 minutes before half time.
A ball over the top was nodded across goal by Robin Le Normand, into the path of Mikel Merino, who headed home his fifth goal in qualification.
La Roja had scored at least twice in their previous 10 games, and their first three chances to extend that run all fell to Borja Iglesias within 10 minutes of the restart, but two were saved by Vutsov before he headed wide what was perhaps the best opportunity of the three.
However, Spain could rely on Merino, who leapt high to score his second header, powering home Alejandro Grimaldo’s cross.
Out of nothing, the Lavovete almost got back into it when Kiril Despodov was played through, and though he beat Unai Simón, his shot trickled agonisingly wide.
Luis de la Fuente introduced Pablo Barrios and Yeremy Pino, who both soon had chances. Then, 11 minutes from time, Pino found Baena, who squared the ball across goal, and the unfortunate Atanas Chernev diverted the ball into his own net on his international debut.
In added time, Martin Georgiev worsened his own debut when he brought down Merino inside the box, allowing Oyarzabal to fire home the resulting penalty.
Having bettered the result of the reverse fixture, Spain have scored 15 without conceding in the group, while Bulgaria have now lost five matches in a row by an aggregate score of 20-1.
Flashscore Man of the Match: Mikel Merino (Spain)