A sloppy Ireland put a poor first period behind them to emerge 28-17 winners over Argentina in an unconvincing warm-up to next week's meeting of the world's top two teams when New Zealand visit Dublin.
Ireland were fortunate to edge an error-strewn first 40 minutes and trailed early in the second period before finding some much-needed composure to pull away from the dangerous Pumas.
The hosts' day, however, was marred by the news that flanker Sean O'Brien, forced off through injury, had broken his arm.
"It was a real test match, really arduous. They were hard at the back, hard off the ruck and hard off the line and really squeezed us," Ireland coach Joe Schmidt said.
"They put some great pressure on our line-out and we struggled, but we got into the game on the back of our scrum, which was very good.
"There's lots to work on. It's not as surprising as, I suppose, it would have been had we had a full preparation or we hadn't had late changes."
Nicolas Sanchez opened the scoring early on with a fine long-range penalty.
Held up on their first raid, Ireland destroyed the visitors' front five in the resulting scrum as halfback Kieran Marmion sniped over for the opening try.
A missed conversion from Sexton allowed Sanchez to restore the advantage two minutes later.
Argentina's Matias Orlando ghosted through midway through the half to set up Bautista Delguy for an easy finish in the corner.
A scrappy Ireland continued to struggle with the wet ball in hand but a dominant scrum again served up a try-scoring opportunity that was ruthlessly taken by centre Bundee Aki.
After Sanchez accepted another penalty shot from distance, Sexton nudged the hosts into a scarcely deserved lead.
Argentina retook the lead again through a Sanchez penalty after the break and it stayed that way until Sexton made it 18-17 close to the hour.
Ireland improved to look far more like the team that had won 15 of their past 16 tests, and a try from replacement scrumhalf Luke McGrath, after a decisive lineout steal, gave them some breathing for the first time.