The Blues lock was sin binned in the 66th-minute for an off-the-ball tip tackle on Donnacha Ryan, with a Tommy Bowe try handing Ireland a 21-15 lead just two minutes later.
But Wales kept their composure and refused to give up the ghost as they hit back through a George North try on 75 minutes to set up Halfpenny's heroic three-pointer.
"It just showed the grit and determination of the boys when Bradley got sin-binned. It probably spurred us on a little bit more," said Hook.
"So many times we've had yellow cards and that's cost us. Sides have scored 10 to 12 points against us and we've lost the game.
"But we kept our composure, especially when we went behind late on. We just ran the ball out of the 22, kept the ball and then Leigh knocked the kick over."
Wales are now preparing to take on Scotland at the Millennium Stadium this Sunday, with Hook unsurprisingly admitting confidence in the camp is high.
A first World Cup semi-final in 24 years had already lifted spirits prior to the trip to Dublin and the nature of Saturday's win has only heightened expectation as Wales chase a third Grand Slam in eight years.
But rather than get carried away with the emotions of what might lie in the horizon, Hook insists Wales will enjoy what was a momentous moment but then focus solely on a Scotland side that should have seen off England at Murrayfield.
"It's the second time I've been part of a winning team in Dublin and it's an amazing feeling," added Hook.
"Everyone knows how well Ireland are doing provincially and everyone expected them to step up internationally. So for us to turn them over on their own patch is superb and will give us confidence for the rest of the campaign.
"It gives us great confidence going into next week, and if we can take that on for the next couple of games, who knows?
"But Scotland will be tough opponents after losing to England. They will have something to prove, so we've got to beware that.
"After the way the boys performed in the World Cup, everyone realises we've got to step up and not just settle for being good players. There's more to come from us and we'll be looking for improvements for next week. We want to kick on and better ourselves."