Owen Farrell kicked four penalties as England won a ferocious encounter 12-6 and passed what Lancaster rated as one of the biggest tests of their character.
"I am delighted to get the win here today," Lancaster said.
"When you have the conditions as they were it was going to be a tight game and down to small margins.
"To come here with a young side and show that kind of matiruty to close the game out was hugely pleasing.
"It is a very difficult to play rugby against experienced players when we have lads on single figures in terms of caps, it is great testament to their maturity.
"As a test of character it was right up there because of the quality of the Ireland side and the ability to get the win."
Under incessant rain, it was what Lancaster calls England's "warrior spirit" which shone through in a game of brutal intensity.
Ireland enjoyed most of the first-half posession but England defended like rabid dogs at times and they led 6-0 at the interval.
Ronan O'Gara landed two penalties to draw Ireland level and with, James Haskell in the sin-bin, England were suddenly up against it.
But England maintained their composure and won that 10-minute period, with Farrell restoring their six-point advantage.
"I put that up there as an absolutely massive win, a huge win," said assistant coach Andy Farrell.
"We have come to Ireland and we have played against a very good Ireland side.
"There was a tricky point in the third quarter but the way we composed ourselves and finished the game - our energy got better, our line speed got better, our composure - was a masterclass of how to handle that last 20 minutes.
"For a young side to play like that in a pressured situation against a team that has been there and done that, and been successful with it, is a credit to everyone."
Two years ago on their last Six Nations visit to Dublin, England failed to match Ireland's intensity and their Grand Slam ambitions were demolished at the Aviva Stadium.
Today, they refused to take a backward step to become the first English side to win a championship game in Ireland since Martin Johnson's Grand Slam team of 2003.
"The lads were desperate for the victory," said forwards coach Graham Rowntree.
"Coming into the Six Nations we had to back up that performance against New Zealand. We did that last week and then we had to do it away from home, because that defines you as a group of players.
"Going forward it will be fantastic to get that under their belts. They upped their game because they knew it would be a massive challenge."