Roberts said:"One team will be packing their bags and one team will be ecstatic about going on to the semi finals.
"It is going to be a great occasion and an epic encounter.
"We have got this far and now it is all about eighty minutes of rugby in the match at the weekend. We must leave absolutely nothing in the tank at the end of the game."
He praised the travelling Welsh fans as an important weapon in the Wales team armoury when they take on the Irish.
Roberts said:"We've got a big travelling circus of fans who are extremely vocal and as players it is a special feeling when you hear them."
He said the strong performances by Wales so far had proved there is no competition for places in the starting XV which bodes well for the future of Welsh rugby.
"We need strength in depth for Wales to progress so it is great to see the competition for places there is right now." He said.
"This weekend will be a step up from the last couple of days because of the huge importance of the game.
"On Saturday the performance of both defences will play a huge part in the outcome.
"Shaun Edwards is adamant that good defence wins test matches and that aspect of our play is standing us in good stead at the moment.
"Shaun is very good and very tough so it is an aspect we work hard on in training.
"Ireland have played some great stuff so far but we have played some great rugby as well so we know this weekend is going to be a great match."