The Wigan Athletic midfielder has finally embedded himself into Ireland reckoning and with experience in the national team he's becoming better, according to his club manager
The Wigan Athletic midfielder also caught the eye during Tuesday's friendly win against Oman at Craven Cottage and his club manager praised McCarthy for his 'composure' in the international arena.
"He is such a mature player and the experience can only help him as a footballer," Martinez said according to Wigan Today.
"He showed great composure in his performance [against Kazakhstan] and I thought he was outstanding on the ball.
"And the stability he provided along with Glenn Whelan probably allowed Ireland to win the game.
"But it doesn’t surprise me he was able to do that because nothing surprises me about James any more.
"I was pleased for him he was able to put in such a good performance with his country watching, but he is such a mature player and the experience can only help him as a footballer."
McCarthy is pushing for a starting place for Ireland's upcoming World Cup qualification matches against Germany and Faroe Islands but is back in club action this weekend against Manchester United.
"This season he really has taken advantage of some excellent work over the summer, he was able to relax, and the way he has started has been outstanding.
"James is such a unique player, a unique type of character on a football pitch, and we know exactly how lucky we are to have him at Wigan Athletic.
"I’m sure he’ll carry on developing into a top, top player at a world-class level," Martinez said.