New Zealand ran in five tries in the first half as they led 31-0 at the break, and added two more in the second period to quieten what was expected to be a hostile crowd in Mendoza.
"The first test (of a season) is always a bit nervy, not knowing where you are at," Foster told reporters. "We knew for us to play with tempo, pace and purpose would be crucial and I thought we did that very well.
"We took the game away from them and probably took the crowd away from them as well."
While the backs dazzled, Foster said the platform laid by his forwards should also draw praise.
"I was happy with the whole lot. Our scrum should be proud with the work they did, and the forwards in general with their work around the park.
"It is a good start. It sets us up well for an interesting game next week (at home against South Africa). Every week is a different challenge but overall I think we have taken some steps in the right direction."
Foster surprised many with his selection of Damian McKenzie at flyhalf ahead of Richie Mo'unga.
"He (McKenzie) looked nice and calm. He controlled the game really well from 10. I am really pleased for him," Foster said.
But the coach was less pleased with the second-half performance as Argentina outscored the visitors 12-10.
"We lost the second half," he said. "We weren’t as efficient with our opportunities. We like to finish strong and we did not do that today.
"That is a credit to their (Argentina's) culture, they did not give up. I thought we opened up too much and they took their opportunities.
"There are some lessons there about when you have an opponent under pressure you have to see it through to the end."
