Full-back James Hook, wing Shane Williams and flanker Dan Lydiate all trained with the squad at Wellington's Newtown Park.
And it means Wales coach Warren Gatland is set to have a full complement of 30 players from which he can choose his starting line-up.
All three players have been sidelined since the punishing Pool D victory over Samoa in Hamilton 17 days ago that put Wales firmly on course to qualify for the knockout phase with world champions South Africa.
Hook suffered a shoulder injury and went off at half-time, Lydiate lasted just 10 minutes before ankle ligament damage sidelined him, while Williams missed appointments with Namibia and Fiji because of a thigh strain.
"You always want your best players fit," Wales assistant coach and skills specialist Jenkins said.
"These guys coming back in gives the squad a huge boost - a huge lift - and there is fantastic competition for places in the squad.
"With Ireland, we play them year in and year out and we know it is going to be a very tough game. They are a very tough side, a very physical side.
"If you win on Saturday, you are in with a shot (of winning the tournament).
"Over the last couple of years the games have been pretty nip and tuck between us. Since 'Gats' came in, we've managed to win two and they've won two.
"We all seem to get on pretty well, especially on the Lions tours. They are a good bunch of boys and a very talented bunch of boys."
Heavy rain over the past two days in Wellington relented as the Wales players headed to training, and although further downpours are forecast, Saturday's prediction is for dry conditions.
"It is a matter of getting the balance right as to when to keep the ball in hand and kicking it at the right times," Jenkins added.
"The weather, I am sure, will play a part, but we will just have to adapt to that. I'm sure these games will be a little bit tighter than they have been in the group stages.
"The boys, in terms of conditioning, are in fantastic shape. We've done a lot of hard work leading up to the World Cup, and that has put us in good stead.
"We knew we were in probably the toughest group of all, and we've managed to come through that.
"The boys are playing some fantastic rugby, they are in good form and they are believing in themselves."
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