It was the flawless way to bow out of cup competitions for Barcelona for Iniesta as he and the rest of the Camp Nou side aim to finish the season with a league and cup double before his exit to China.
Coutinho's penalty after Clement Lenglet handled the ball in the area helped Ernesto Valverde's side finish emphatically and they were soon able to celebrate with the cup which had their name on it from the start - and recently always seems to. It doesn't hide what happened in Roma, but it's an important title. "But at the beginning of the season anyone would have signed for a double".
Suarez scored his 31st and 32nd goals of the season while Iniesta delivered one of those effortless displays, in which at times he was virtually unplayable.
Coutinho wrapped up the scoring 21 minutes from time.
"Barcelona has been superior in everything, they have extra-terrestrial players", Montella said. "We worked in an organised way". Spain's King Felipe VI smiled and saluted the fans after the anthem.
It took just 14 minutes for Barcelona to take the lead and it was a simple goal as Jasper Cillessen lofted a superb long ball down the field which picked out Coutinho.More news: Thunder Drop Game 2 to Jazz in Playoff Series
More news: Tiwari demands apology from Rahul, Kejriwal
More news: Unfair trade practices impede US, global growth: US Treasury's Steven Mnuchin
Messi slammed home the second after good work from Jordi Alba with Suarez adding another, before Iniesta netted from a tight angle.
Messi could have had a second were it not for an incorrect offside call and then a cynical foul by Sergio Escudero, for which he was lucky only to receive a yellow card.
The tie was effectively put to bed in the 40th minute, Suarez exchanging passes with Messi in the number 10 pocket before finishing low past Soria.
The holders quickly found their stride and went close to breaking the deadlock on seven minutes with a free-kick from Messi that was expertly saved by David Soria to his left.
BC-SOC-Copa del Rey Final, 1st Ld-Writethru, 429 Barcelona easily wins historic 4th straight Copa del ReyAP Photo XDMV137, XEL118, XEL117, XEL119, XDMV119, XDMV125, XEL124, XEL135, XDMV152, XEL137, XDMV156Eds: Updates with more detail, photo links.