The Roman, meanwhile, came into the contest at Madrid's Wanda Metropolitano with nothing to fear, as Sweden had already locked down second in the group and the Balkan side's only chance of advancing lies in a potential playoff.
Apparently undistracted by rumours that coach Robert Moreno will be leaving in favour of previous incumbent Luis Enrique, La Roja overwhelmed the visitors from the opening whistle, reports Efe news.
Spain had 75 per cent possession, outshot their opponents 21-6 and made 863 passes to Romania's 296.
The Spanish attackers ran rings around the Romania defense and even before Fabian Ruiz scored in the 8th minute to make it 1-0 for the hosts, Santi Cazorla hit the post and Jose Luis Gaya had a goal disallowed.
Romania's only opportunity in the first half was the result of a defensive miscue that left striker George Puscas alone in front of Spain's goal, where Kepa proved equal to the task, while the referee ignored the visitors' plea for a penalty after an encounter between Dani Carvajal and Florinel Coman.
Gerard Moreno, off to a great start with Villarreal in LaLiga, took a giant step toward winning a spot on Spain's Euro 2020 with a pair of goals just 10 minutes apart - in the 33rd and 43rd - with support from Alvaro Morata.
Moreno also initiated the play that resulted in Romanian defender Adrian Rus' own goal in the 45th minute to give Spain a massive 4-0 advantage.
Job done, La Roja eased up a little in the second half, though they remained dominant and almost all of the handful of threats Romania managed to pose were the consequence of Spanish errors.
Sergio Ramos and Morata had each chances for the fifth goal, but it was Mikel Oyarzabal, sent in for Moreno in the 56th minute, who completed the rout with a great strike in stoppage time.
Spain win Group F with 26 points on eight wins and two draws, five points ahead of Sweden.
( With inputs from IANS )