Coach Eddie O'Sullivan highlighted a lack of discipline as the main reason behind Ireland's 22-20 defeat to Argentina in Santa Fe on Saturday.

A last-gasp Felipe Contepomi drop goal sealed victory in the first Test for the Pumas and O'Sullivan believed that, despite a good performance from his relatively inexperienced side, a high penalty count eventually made the difference.

"I think the big problem was discipline," he said.

"I talked to the players and said they played well but discipline was the problem.

"We gave away too many penalties, especially in the second half.

"In the first half, we were controlling the game. Argentina took the upper hand after the break and took their opportunities very well.

"But in the end either side could have won it."

O'Sullivan was full of praise for match-winner Contepomi after the Leinster fly-half bagged 17 points.

But the 48-year-old was also pleased with an encouraging display from former rugby league star Brian Carney after the winger claimed a try on his Ireland debut.

"He (Contepomi) had a super game," O'Sullivan added.

"I said yesterday (Friday) that he could be the difference between the two teams and he was.

"But Carney did a good job and it was an inexperienced backline. Despite some mistakes, I'm happy with his performance and I told him that"

Scrum-half Isaac Boss agreed with O'Sullivan's assessment that a sloppy second half cost Ireland the game.

"It started so well, so positively. In the first half we did a lot of things well and controlled Argentina," he said.

"But in the second half we made a lot of mistakes and they won with a bit of our help."

Simon Best, who skippered the side on his 17th cap, insisted the result will have little bearing on the two side's World Cup clash in Paris on September 30.

"They will be very different teams because there are a lot of players missing," he said.