And the huge crowd went home happy, but had to endure a nervy final 20 minutes after Wales failed to turn their dominance into points.
Coach Gatland explained afterwards, "We wanted to be more ruthless in our approach, but unfortunately we weren't. We created a lot of chances and line breaks and e should have put the game away.
"But we simply weren't clinical enough. We have to learn from our mistakes and in the first-half we kept kicking the ball away.
"We felt physically that if we kept playing with tempo their forwards would struggle and tire later on.
And the Kiwi coach would have been as nervous as anyone as Samoa pulled to within a converted try over a monumental win after Mapusua scored an interception try on the hour mark.
Gatland said; "It was a little bit too close for comfort in the end and we put ourselves under pressure. We made 11 line breaks to their two and our finishing wasn't good enough.
"We should have put the game away comfortably. The game should have been out of sight by the time they got their interception try - that was a 14 point try because if he hadn't have caught it we would probably have scored.
"But we have come away with a win."
Captain, and Man of the Match Ryan Jones commented: "It was about as tough as it gets in Test match rugby. The Samoans gave everything and really hit hard.
"But our boys dug deep for the victory that we wanted and needed. There is a courage, strong work rate and work ethic with my guys and it was great we kept them out in the last five or six minutes.
"We need to look at cutting out the mistakes. We have been offering so much, but not quite delivering - we haven't had that clinical edge in our game.
"It has been a case of the last pass or the last phase letting us down.
"But fair play to the Samoans, they came together on Sunday and put a fantastic performance together.
"The game against Argentina is going to be very difficult and we have got to take more ownership of the game and cut down on the errors.