Fernando Torres made a timely return to form with two goals as Spain ended Republic of Ireland's European Championship adventure with an emphatic win in Gdansk.
Torres struck after just four minutes, riffling home after nipping the ball away from Richard Dunne.
The Irish clung on for the remainder of the first-half, but played second fiddle after the interval, as David Silva and substitute Cesc Fabregas netted, either side of Torres' nonchalant second.
The win leaves Spain level on points with Croatia going into the pair's meeting on Monday, while Ireland are left to reflect on a campaign, which will end against Italy on Monday, where they appeared out of their depth from the first whistle.
Having enduring contrasting fortunes during their respective opening group games, both managers opted to make just one change apiece, with Spain opting to start with a striker in Torres, while Giovanni Trapattoni selected Simon Cox ahead of Kevin Doyle.
Ireland had seen their first major finals campaign get off to the worst possible start against Croatia in their opening game, conceding a goal within three minutes on that occasion, and despite seeing Cox force Casillas into a smart early save, their lack of early concentration contribute to their downfall again.
When Dunne dawdled in possession, Torres nicked the ball away before smashing the ball into the roof of Shay Given's net in the ruthless nature the Spaniard has seldom shown produced during his Chelsea career.
Torres came close to doubling the World and reigning European Champions' lead just minute later, when Xavi's cross-field ball found Alvaro Arbeloa, whose first-time cross found the onrushing forward, who could only side foot wide.
Having selected a side to stifle the Spanish, rather than to take the game to Vicente Del Bosque's side, the capacity Irish crowd could have been forgiven for fearing the worst, as a midfield again spearheaded by Xavi and Andres Iniesta dictated proceedings.
But Trapattoni's side hung in the contest, with Given saving from Arbeloa from range, and Xavi, before watching Xabi Alonso's volley bounce wide and touching over Iniesta's drive.
However, the experienced Irish stopper played a big role in the move that saw Spain put the game beyond their opponents, less than four minutes into the second half as Given's weak punch from Iniesta's shot fell to Silva, who twisted and turned before finding the far corner.
Spain were threatening to turn their dominance into a rout, with Given saving expertly from Xavi's point blank effort.
In similar fashion to their first half performance, Ireland rallied, but could stem the flow no more with 20 minutes to go, as Silva released Torres, who drew Given before calmly finding the corner.
Torres was immediately replaced by Fabreagas upon his second goal, and the Barcelona midfielder capped his cameo with Spain's fourth, smashing home from Silva's corner after some slack Ireland defending.
Spain know a win against Croatia in their final group game will give them top spot in Group C, while Ireland face Italy in the knowledge they will play no part in the knock-out stage.