Ireland, who should have British Lions centre Brian O'Driscoll back for the Dublin clash, will provide Wales with a far more accurate gauge of their recent progress than a new-look Scotland while O'Kelly is aware of the challenge awaiting his team.
"The Welsh are a very physical side, but we have got to meet them head-on," said the Leinster forward.
"We lost to France while they will go into the match with a lot of confidence after their win over Scotland.
"We will take a look at how they played against the Scots - from what I have been told they looked very good. They played very well and we will have to bear that in mind.
"But we go into Sunday with a clean sheet and everything to play for. They will expect the usual passion from us and we won't let them down."
France strolled to victory on Saturday despite showing only glimpses of their destructive brilliance, with the tries from Vincent Clerc and Pascal Pape being pulled straight out of the top drawer.
Ireland also exhibited flair in attack, not least Ronan O'Gara's chip and gather which led to Anthony Foley's try - but O'Kelly felt his side's decision-making let them down, although he was full of praise for the French.
"It was a hard game. France have some great ball players and run really good lines. If you are not focused on what they are doing they will rip you to shreds. We lacked a little bit of decisiveness and we will have to improve on that," he said.