Ireland coach Joe Schmidt bemoaned the sin-binning of Johnny Sexton just before the break was a turning point in his side's 22-9 defeat to Wales in the RBS Six Nations on Friday evening.
The defeat ends Ireland's hope of winning the championship, with England to come in the Aviva Stadium next weekend.
The visitors were leading 6-5 at the Principality Stadium when Sexton - who had been off the pitch for nine minutes earlier in the half following a head injury - was penalised for not rolling away at a ruck on the Irish line.
"The yellow card was crucial - 10 points in 10 minutes," Schmidt said.
"I feel a bit sorry for Johnny. He's trapped in by three players and it's hard to get out.
"But when that happens close to the line that sometimes happens.
"You've got to (win) the fine margins when you're playing a Welsh side as good as they are, and as desperate as they are, and we did not do that.
"Wales played really well - their set-piece and defence was strong, and they attacked well - and we weren't accurate enough."
Welsh coach Rob Howley hailed an "outstanding" Wales team performance.
"I'm just very proud of the players," Howley said.
"I thought it was an outstanding performance. We wanted an 80-minute performance.
"We feel, internally, we should have beaten England, but international rugby is about fine margins and we've come up short.
"The players have been outstanding since Scotland, they've been very honest in their appraisal about the way they played in the first 15-20 minutes of the second half at Murrayfield.
"They wanted to go out in front of the best supporters in world rugby and give a performance they can be proud of.
"They certainly did that. They outscored one of the best sides in world rugby three tries to nil and we kept them out defensively.
"We have felt a lot of hurt, but they deserve a lot of credit for what has happened in the last couple of weeks because the results have not gone our way."
George North was among those Welsh players singled out for criticism for his performance in Edinburgh.
But the 24-year-old Northampton Saints winger answered his critics, with two tries taking his Test tally to 30 in 68 games.
The first was particularly memorable as he ended a fluent Welsh move by brushing past Ireland pair Keith Earls and Simon Zebo to power over.
"He's a quality, world-class international player," Howley said.
"We all have bad games and George is the first one to put his hand up after the Scotland game.
"He said: 'Look I need to do better' and he certainly did that.
"He showed ambition, he had a number of touches and when he gets five metres out, he's very difficult to stop.
"The try down the short side in the second half was very smart play.
"We want him on the ball as often as possible and Liam Williams on the other side made some important tackles as well.
"We played quite smart but we're a bit disappointed with the contact area.
"I know they had a yellow card but the penalty count was 10-4 and we did not feel the benefits in that area."
