Croatia, for whom Ivan Rakitic was making his 100th appearance, rarely got to grips with their opponents and conceded three times more in the second half through Rodrigo Moreno, Sergio Ramos and Isco.
After a disappointing World Cup, Spain have bounced back as a new era under Luis Enrique begins, with two back-to-back victories against formidable opponents in the form of England and Croatia, both of whom had impressive showings in Russian Federation.More news: This may be our first look at OnePlus 6T in flesh
They'd have seen Spain edge out England 2-1, with a largely impressive opening display under new boss Luis Enrique - and will now be raring to take on the Spanish themselves at Estadio Manuel Martinez Valero in Elche.
Asensio, who was not among the starters against England, also set up Rodrigo's goal early in the second half with a ideal through ball behind the defence. Croatia and England are both pointless after one game.
Under the guidance of new head coach Luis Enrique, La Roja have adopted a new tactical approach that saw Marcos Alonso, Saul and Iago Aspas all play a starring role against the Three Lions within a new-look starting XI.More news: Judge strikes down bill to reduce Toronto council size
The two teams last met at Euro 2016 when Croatia came away with a 2-1 win after overturning Spain's lead. Bustling forward Lukaku was bundled over by Sverrir Ingi Ingason in the 28th minute and the referee immediately pointed to the spot, with Chelsea playmaker Hazard calmly sending Hannes Halldorsson the wrong way with the resulting penalty.
In other Uefa Nations League games, England edged Switzerland 1-0, Belgium beat Iceland 3-0, and Poland and Ireland played out a 1-1 draw. Yet despite missing one of their main playmakers, there was no lack of creativity in the side.More news: Top 5 moments from the Vikings’ Week 1 win over the 49ers