Wales crushed Ireland's dream and reached the World Cup semi-finals for the first time since 1987 with an impressive display in Wellington.
Wing Shane Williams squeezed over for Wales' early opener, Keith Earls responding in kind after the break.
But in-form scrum-half Mike Phillips' clever dive and centre Jonathan Davies' burst past prop Cian Healey settled the contest in Wales' favour.
Rhys Priestland added seven Welsh points to Ronan O'Gara's five.
Ireland produced a performance that justified their status as Pool C winners against the Pool D runners-up, but Wales now await news of who they will face in the semi-finalsv - England or France.
Outstanding flanker and captain Sam Warburton's side proved equal to the challenge as they held out Irish dangermen such as Brian O'Driscoll, Sean O'Brien and Tommy Bowe.
Lock Luke Charteris epitomised the Welsh effort, making 16 tackles before being replaced by Bradley Davies at the break.
Wherever Ireland threatened, Wales seemed to have enough numbers and commitment to cope other than when wing Earls made the most of his chance.
The Welsh line-out also stood up to the notable challenge of Paul O'Connell and Donncha O'Callaghan to such an extent that Alun Wyn Jones and Bradley Davies came out on top as the game wore on.
At the scrums Ireland were unable to repeat the efforts that Australia found so punishing in the pool stages and Wales go into the last four with a solid platform and potent attacking threat.
Jamie Roberts was again the focus of Welsh efforts with ball-in-hand, on one occasion running over Gordon D'Arcy while regularly making telling inroads.
And with Priestland guiding the effort and Phillips continuing a rich vein of form, Wales proved superior behind to the O'Gara-O'Driscoll axis from which Ireland have relied in the past decade.
Wales last reached the last four in the inaugural 1987 event, finishing third on that occasion after beating Australia in the play-off while Ireland must wait another four years to again attempt to do so for the first time.
Gatland's men hope to go at least one better at this tournament after leading the way among the nothern hemisphere challengers.
Wing Williams extended his Wales record try tally to 56 in the third minute as they began with an assurance that belied the occasion.
They patiently built a multi-phase attack in which Jamie Roberts took a high ball going forward and Toby Faletau also made ground before Halfpenny put Williams over in the right corner.
Video referee Giulio de Santis confirmed the score and Priestland converted from the wide angle.
Indiscipline and Ireland's ability to build pressure from it denied Wales the chance to capitalise on their good start.
In quick succession Faletau went over the top at a ruck, George North failed to roll away from a tackle and Dan Lydiate was caught offside at a breakdown.
But Ireland were unable to break down Wales' defence as they settled for a series of attacking line-outs instead of kicking for goal.
North pulled off a crucial tackle on Bowe that thwarted one Irish attack.
But when Roberts again put Wales on to the front-foot, O'Driscoll intercepted Phillips' pass to launch Ireland's best attack of the opening half in which D'Arcy's dummy and run underlined the threat to Wales.
However, Williams somehow managed to hold powerful flanker O'Brien off the floor as the flanker crossed the line to deny Ireland a first try.
O'Driscoll set off again after taking Priestland's up-and-under to give Rob Kearney a run and when Wales again fell foul of the tackle laws, this time O'Gara took Ireland's first points from the penalty.
Halfpenny restored Wales' seven-point advantage with a long-range penalty while O'Gara sent two kicks into touch-in-goal as the tension mounted.
Ireland drew level in the 44th minute when Stephen Ferris and Bowe combined to give Earls the time and space to cross at the corner for another try settled by the video ref and O'Gara converted.
But five minutes later Phillips stole away on the blindside after Alun Wyn Jones' drive before beating D'Arcy and evading Bowe's tackle to dive over, also securing the video ref's approval.
Priestland could not convert and his chance to put Wales eight points ahead after Cian Healey was penalised at a scrum rebounded off and upright to leave the contest on a knife edge.
Wales went further ahead when centre Davies made the most of Healey's appearance in the midfield defence to fend off the prop and burst clear to score.
Priestland converted to put Wales 12 points ahead with 15 minutes remaining.
Ireland's attempt a response saw replacement scrum-half Eoin Reddan conjure a superb pass to O'Brien.
But the Irish flanker was halted three metres short and knocked on before Healey was penalised at the scrum, allowing Wales to clear.
Ireland threw all they had left at Wales in the closing stages, but the defence coached by Shaun Edwards proved equal to the task.
Wales: Leigh Halfpenny (Cardiff Blues); George North (Scarlets), Jonathan Davies (Scarlets), Jamie Roberts (Cardiff Blues), Shane Williams (Ospreys); Rhys Priestland (Scarlets), Mike Phillips (Bayonne); Gethin Jenkins (Cardiff Blues), Huw Bennett (Ospreys), Adam Jones (Ospreys), Luke Charteris (Dragons), Alun Wyn Jones (Ospreys), Dan Lydiate (Dragons) Sam Warburton (Cardiff Blues, capt), Toby Faletau (Dragons).
Replacements: Lloyd Burns (Dragons), Paul James (Ospreys), Bradley Davies (Cardiff Blues), Ryan Jones (Ospreys), Lloyd Williams (Cardiff Blues), James Hook (Perpignan), Scott Williams (Scarlets).
Ireland: R Kearney (Leinster); T Bowe (Ospreys), B O'Driscoll (Leinster, capt), G D'Arcy (Leinster), K Earls (Munster); R O'Gara (Munster), C Murray (Munster); C Healy (Leinster), R Best (Ulster) or S Cronin (Leinster), M Ross (Leinster), D O'Callaghan (Munster), P O'Connell (Munster), S Ferris (Ulster), S O'Brien (Leinster), J Heaslip (Leinster).
Replacements: S Cronin (Leinster) or D Varley (Munster), T Court (Ulster), D Ryan (Munster), D Leamy (Munster), E Reddan (Leinster), J Sexton (Leinster), A Trimble (Ulster).
Referee: Craig Joubert (South Africa).
Assistant referees: Wayne Barnes (England), Romain Poite (France)
TMO: Giulio de Santis (Italy)
