Cardiff - Wales blew the Six Nations race wide open by battling to a thrilling 23-16 victory over Ireland at the Millennium Stadium on Saturday.
Five Leigh Halfpenny penalties, a Dan Biggar drop-goal and a try from replacement Scott Williams ended Ireland's hopes of a first Grand Slam since 2009.
Joe Schmidt's side had Wales worried with a penalty try 10 minutes from time converted by Jonathan Sexton, who also hit three first-half penalties, but Halfpenny brought Ireland's 10-match winning streak to an end with a decisive late penalty.
The win moves Wales level on points at the top of the Championship with one weekend to play.
Wales set the tone for an early onslaught by reclaiming the kick-off after Ireland full-back Rob Kearny was beaten in the air.
Warren Gatland's men went on the attack and forced Ireland to creep offside, and referee Wayne Barnes was quick to give Halfpenny a nerve-settling shot at goal.
He converted to give Wales a 3-0 advantage after just two minutes.
Ireland's troubles continued from the restart when Jonathan Davies fended off Sexton to spark another promising Welsh attack.
Schmidt's premier playmaker only picked himself up to give away a penalty for not rolling away, which Halfpenny converted to extend their lead.
Ireland had been given two warning shots by Halfpenny, but had not learned their lesson and offended again four minutes later when a bruising hit from Gethin Jenkins forced the returning Jamie Heaslip to hold on in the tackle.
Halfpenny carried on his imperious kicking form to put Wales 9-0 ahead from the halfway line.
Ireland's indiscipline was starting to become an issue for Schmidt and Jack McGrath received a stern word from Barnes after again refusing to release at a tackle.
Halfpenny made it four penalties from four before Ireland finally got a foothold in the game.
They made their first foray into Welsh territory after 15 minutes and won a kickable penalty 20 metres out, but Sexton's nightmare start continued as he pulled his kick wide.
But he did get his side on the scoreboard a minute later after Scott Baldwin hit Tommy Bowe with a high tackle.
Both sides had been warned for their first-half infringements, but Wales had not heeded their warning and skipper Sam Warburton was sent to the sin-bin for not releasing after a tackle.
Sexton shook off his early wobbles to notch Ireland's second three-pointer, and added a third after Biggar had restored the nine point lead with a well-timed drop-goal.
Ireland came out firing in the second-half, but Wales were just as staunch in defence.
Gatland's men survived a total of 46-phases of pressure just metres from their line, but were allowed to clear when Sexton dived in at a resulting ruck.
Wales took their momentum back downfield and made some inroads of their own, before replacement centre Scott Williams sent Ireland's Grand Slam hopes into disarray.
He latched onto Biggar's pass before he sold Bowe a dummy and outpaced the scrambling Jamie Heaslip to score.
Halfpenny could not convert and the Six Nations front-runners made them pay.
They battered the Welsh line once more but their 17th knock on thwarted another promising attack.
But they made no mistake from the next wave. Wales had given a penalty away in the build-up, and referee Barnes was forced to award a penalty try when they dragged the rumbling maul down over the line. Sexton converted and Welsh nerves were jangling with 10 minutes left.
But Halfpenny handed Wales a seven-point lead with his fifth penalty four minutes from time and the home side held on to deny Ireland.
Wales 23 (Scott Williams try; Leigh Halfpenny 5 penalties, Dan Biggar dropped goal)
Ireland 16 (Penalty try; Jonathan Sexton conversion, 3 penalties)