Ireland then struck the post with a penalty of their own on five minutes but a try came two minutes later as Jacob Stockdale picked up Johnny Sexton's flick to the wing and crossed over, though the latter's subsequent conversion attempt sailed wide.
Wales then surged back into the lead on 10 minutes when a turnover led to Gareth Davies going over and Halfpenny adding two more points from the boot, an advantage built upon further with another penalty on 30 minutes.
However, the hosts got three points on board as Sexton finally got a penalty over and ended the opening 40 minutes ahead when their pressure finally gave way to a try, Aki bursting through from a metre out and the kicker adding the extras.
Ireland added seven more points on 44 minutes when a turnover saw Keith Earls and Rob Kearney combine to enable Dan Leavy to cross over before Sexton converted, and another try came nine minutes later as Cian Healy barged over from close range.
Just after the hour mark, Wales reduced the deficit to seven points as Aaron Shingler went over in the corner and Halfpenny added the finishing touch with his boot, but Ireland pulled further ahead on 72 minutes through Conor Murray's penalty which came off the post.
The visitors made it a tense finish when Scott Williams and Josh Navidi combined to release Steff Evans who duly went over, with Halfpenny converting, but Ireland made sure of victory late on through Stockdale's galloping try.