For all their endeavour in defence, Ireland struggled constantly to cope with the torrent of Spanish attacks as Chelsea's Fernando Torres proved he is back to his best with two clinically-taken goals.
Having decided the EURO 2008 final with the winning goal against Germany, Torres netted either side of David Silva’s second-half strike before his replacement, Cesc Fabregas, added the fourth seven minutes from time.
With 66 per cent ball possession, 26 shots on goal, 20 of which were on target, Ireland goalkeeper Shay Given had a busy night as Spain dominated while Ireland managed just six shots on goal in total.
The win puts Spain top of the group on goal difference and level on four points with second-placed Croatia, who Vicente del Bosque's world champions face back at Arena Gdansk again on Monday.
Having suffered their second defeat after losing 3-1 to Croatia on Sunday, Giovanni Trapattoni's Ireland will exit after the group stages. Italy, who drew 1-1 with Croatia earlier, have two points in third and can still progress if they beat Ireland in Poznan the same day, but Gli Azzurri are reliant on either Spain or Croatia winning in Gdansk.
"That is a very good win for us," said Spain coach Del Bosque. "We brought in Torres to score goals, which is what he did and if we stay with this defensive line we will have things easy. It will be dangerous to play for the draw against Croatia and we won't play for the draw."
Fast start from Spain
Having used a 4-3-3 formation against Italy without a recognised striker, Del Bosque elected to start Torres at the expense of Barcelona's Fabregas. The Chelsea star rewarded the faith with the opening goal after just four minutes.
Buoyed by the legions of green-clad fans, who clearly outnumbered the Spanish supporters at the stadium and sang until the end, Ireland battled forward, but any rare first-half forages into the Spain half were quickly snuffed out.
A heavy tackle on Andres Iniesta earned Ireland captain Robbie Keane the game's first booking on 36 minutes and Glenn Whelan followed just before the break for a foul on Silva as it finished 1-0 at the break.
Fabregas finishes the rout
Trapatonni brought on Stoke City's Jon Walters for Simon Cox up front at half-time, but there was no stemming the tide of Spanish attacks. A long-range shot from Iniesta was parried by Given, but fell into Silva's path, who jinked his way around several defenders to roll his shot calmly past Given four minutes after the break.
After Given pulled off more heroics to deny Xavi Hernandez's corner shot, Ireland lifted their tempo with a series of attacks as Spain goalkeeper Iker Casillas was pressed into service.
The threatened third goal came when Silva released Torres, who raced away from Dunne and slotted home his shot on 70 minutes to give Given no chance, before the Spaniard made way for Fabregas four minutes later.
The Barcelona star, who scored the equaliser against Italy, again showed his class as he drilled home his shot from a tight angle for Spain's fourth.