Wales led the game a minute into injury time, but a last-minute dropped goal to Ireland's Ronan O'Gara kept his team on track for a magnificent Grand Slam.
England referee Steve Lander found himself at the centre of controversy as the gallant home side were robbed of a possible chance of victory at a packed Millennium Stadium.
Wales took the lead in injury time with a 45m dropped goal from Stephen Jones, before Ireland hit back within 30 seconds as O'Gara followed suit to edge the men in green one point ahead.
Wales v Ireland minute by minute
There was still enough time for Wales to mount one last attack and when Ireland winger Justin Bishop launched himself at the ball with one hand every Welsh fan in the ground expected Lander to award a penalty for a deliberate knock-on.
He signalled for the offence, but Wales charged on into the Irish 22
through Colin Charvis. The ball came back to Jones and the outside half lined up another dropped goal attempt to win the game.
This time, though, Denis Hickie raced up to charge down the kick and
Ireland's Grand Slam dreams lived on.
Two tries in five minutes either side of the interval by backrower Keith Gleeson seemed to have set Ireland on the way to another comfortable victory and at 19-7 behind Wales looked like having a tough time for the remainder of the second half.
But the home players stuck to their task, clawed their way back into
contention with two superb tries and then sent the Welsh fans into
raptures with that injury time dropped goal from Jones.
David Humphreys kicked three penalties in the first half, but his
opposite number Jones gave Wales the lift they needed midway through the first half when he took the ball moving left in the Irish 22 and bounced through two tackles to reach the corner flag.
A wayward clearance out of his 22 by Rhys Williams allowed Geordan
Murphy to peg Wales back with a corner kick and then the full back used some magical footwork to break down the home defence wide out to give Gleeson the first of his tries two minutes before the break.
A minute after the restart Gleeson was at it again, this time taking a Humphreys pass to score after Matthew Watkins had seen his clearance kick from under his posts charged down. All of a sudden Wales were in danger of falling apart as the Irish threatened to go on the rampage.
But two special tries from Martyn Williams and Gareth Thomas, taking him to 29 for his country, both converted by Jones, brought Wales back to within a single point with 15 minutes to play.
Wales: Tries: S Jones, M Williams, G Thomas; Cons: S Jones 3; DG: S
Ireland: Tries: K Gleeson 2; Pens: D Humphreys 4; DG: R O'Gara.