Gatland's visit to Hamilton didn't appear to be heading for a happy return at halftime when his side were 10-6 behind against the rampaging South Sea Islanders, but Wales overturned the deficit to remain on course for the knock-out stages.
"I thought we showed some great character," said Gatland after Wales' first World Cup appearance in his home town. "A few years ago, or 12 months earlier, we might not have won that game. We will dissect the performance over the next couple of days and see where we can improve.
"In the first half, we tried to play a bit too much rugby, but our whole World Cup was about going out in that second half and digging deep. And they did that.
"I thought our conditioning was great. The longer the game went on, the stronger and fitter we looked. We knew this was a must-win game, and (a quarter-final place) is in our own hands isn't it?"
Wales had plenty left in the tank as the match reached its climax, but the Samoans, who only had four days turnaround after playing Namibia, visibly wilted as Wales turned the screw in the dying minutes.
There are a couple of injury concerns as key back James Hook and dynamic flanker Dan Lydiate didn't make the second half with shoulder and ankle injuries respectively.
"(Lydiate) has rolled his ankle. He was a big loss to us defensively," said Gatland. "The number of tackles he makes, he's a player that doesn't get a lot of recognition. He cannot put any weight on (the ankle) so we will see in the next 24 to 48 hours."
Captain Sam Warburton paid tribute to the defensive effort put in at the coalface by his players. "I don't think you can fault the attitude of the players," said Warburton, who dedicated Wales' win to the families of four miners killed at Gleision Colliery near Pontardawe earlier this week.
"I think at half-time there was no panic. We knew we had the fitness levels to take it to 80 minutes. We said if we lost the chances are we were probably going home, so there was a lot of pressure on the boys.
"Both sides didn't disappoint - we knew it was going to be an immensely tough battle. Samoa are very physical, and it was a tough game for us.
"We wanted to keep the ball in play as much as we could and back our fitness levels towards the end of the match.
"Leigh (Halfpenny) came on and added some great momentum to the side, and Shane finished it off as we've seen him do a million times before. If our backs get a sniff, they are pretty handy."