Wales were well on top in the early exchanges and Ryan Jones was denied a try by the video referee before Jonathan Davies was adjudged to have got the ball down after a superb offload by Rhys Priestland, who hit the post with the conversion and a penalty.
Ireland hit back with a Rory Best try after a great Tommy Bowe dummy just before halftime only for Davies to grab his second touchdown after the break as Wales led.
Bowe put the Irish clear with his own try on 68 minutes but George North went over for Wales late on to move within a point.
Stephen Ferris joined Bradley Davies in the sin bin as both were punished for dangerous tackles and Halfpenny slotted the penalty through the posts as Ireland failed to gain revenge for their World Cup quarter-final defeat.
