Lopetegui’s side started the match in startlingly naive and passive fashion, with Jordi Alba raiding their right flank where utility defender Nacho was playing at full-back.
Alba provided the opening goal when he cut-back to Coutinho from the bar-line, and the former Liverpool man swept past Thibaut Courtois.
Saurez won the penalty he converted, darting across Rapheal Varane with a near-post run. Despite obvious contact from the defender, referee José María Sánchez Martínez waved away appeals for a penalty before changing his decision after consulting VAR.
Lopetegui switched to a back three at half-time with Casemiro moving back into defence, and Lucas Vazquez replacing Varane.
The alteration paid dividends when Marcelo got on the end of Isco’s cross from his new, advanced wing-back position and turned home at the second attempt.
Karim Benzema headed over unopposed from six yards, and Real rued not capitalising on that short period of dominance as Barcelona slowly re-established their superiority.
The game was effectively over when Suarez showed magnificent reflexes and striker’s instincts to turn home Sergi Roberto’s cross with a stunning header from fully 14 yards.
A sumptuous dinked finish over Courtois secured the hat-trick, before fine work from substitute Ousmane Dembele assisted Vidal’s headed goal to complete the rout.