Swansea made it back-to-back victories in the match, following up last year's success at the Liberty Stadium, which pleased Lancaster.
"We are delighted with the win," he said.
"It was such a big occasion for our players and they performed really well.
"We knew Cardiff would be strong but it was up to us to rise to the challenge.
"They have had a good season and were on a high after gaining promotion, that said we have had one of our best ever years and were confident in our ability coming into today.
"It really is a great occasion for the players, to play in such a fantastic stadium.
"There were a lot of regional rugby representatives here from the Ospreys and it's great for the lads to be able to demonstrate their talent to such teams."
"It's been a long season for us, a lot of the guys play premiership rugby and the volume of games has taken it's toll on the players, there were a lot of tired bodies towards the end."