They had only needed 15 points to beat Australia; instinctively they would have worried that they were going to need a few more than that to beat their Six Nations' rivals.
Curious how the mind can play tricks on the most experienced of sides.
So instead we saw Ronan O'Gara turning down three kickable penalties. There was a certain logic to it - they were wide out on a notoriously difficult ground for kicking - but at 0-0 rather than 7-0, he would have been more inclined to take his chances.
While it might have been a stretch to say Wales were in complete control, they did have Ireland scrambling for answers to problems they had not encountered in Pool C.
In particular, they did not know how to deal with the line-speed of the Welsh in defence. For the first time, Sean O'Brien, Jamie Heaslip and Stephen Ferris were being stopped behind the advantage line, sometimes a long way behind.
That forced them closer to the flanks where they hoped to find greener spaces. Wales responded by twice shovelling Heaslip over the left-hand touch.
Ireland did not want for ball, but their failure to get on the front foot meant O'Gara was kicking too often out of desperation, rather than pattern. Twice he pushed the ball dead and at other times Leigh Halfpenny and Rhys Priestland had too easy a time mopping up.
It wasn't a night to savour the Munster veteran. After both sides had swapped tries early in the second half, O'Gara threw an awful pass that was the final straw for coach Declan Kidney.
On came the livelier Jonathan Sexton. By then it was too little, too late.
Wales forwards had an iron grip and they weren't going to let go. They played with a passion that was close to manic.
It's tempting to list the heroes, but there'd be eight of them, so best just to acknowledge that they are epitomised by their young captain, the indefatigable Sam Warburton.
He'll now lead Wales to the Promised Land. A semifinal, a place Wales have never been in his lifetime.
Don't bet against them going one step further.
