"The key thing for me was the way we responded after they scored," Mariner told the media.
"At half time it was goalless and we said 'let's go for this' because we had something to build on - and they went and scored straight away.
"It was a good goal, well taken but we showed what we are about because we got straight back at them.
"I was delighted with Damien for the way he finished from the rebound because he had to volley it up in the air, he kept his cool in a difficult situation. He did that and did it well."
Swansea boss Paulo Sousa had no complaints with the penalty but was left fuming by referee Keith Hill's call for a retake.
He said: "Everyone in the ground could see what happened. I have watched a replay of it since and the keeper's foot is on the line.
"Dorus did well to save to save them both and showed what he can do when he is called upon although we have not needed him for the past month or so.
"We dominated the game for long spells but we needed two or three touches on that pitch when normally we would only need one and we were not able to play the way we wanted - and pass it quickly."