"In the first half, I think we lost the battle at the breakdown," said Roberts.
"They (Samoa) seemed to target it, and we weren't good enough in the contact area and we kept losing the ball. Maybe in that first half we also tried to play a bit too much. That is always the danger, certainly when the sun is out, and I suppose we were guilty of that.
"We came out for the second half and we knew it was going to take a big defensive effort. They are pretty big guys, the Samoans. There was some great goal-line defence from us, and not to concede a point in the second half was a pretty special effort. We won ugly, but it was a win.
"It's a bit of the opposite to last week (against South Africa) to be honest. It wasn't a champagne performance by a long way, but the win was vital.
"As soon as the final whistle went last week, the preparation for this game was all about winning. That was all that mattered.
"Samoa certainly fly with ball in hand. They are really powerful guys, but our fitness showed in the last 20 minutes, which was pleasing.
"There was no panic at half-time. We had just conceded a try, but we had spoken about it in the week that we might have been down by a try.
"They are a good side - you are not going to put 30 or 40 points on them - and we regrouped at half-time. We wanted to play a direct, good territorial game, and our defence was very strong. Defensively, we can take a lot out of it."