The midfielder was part of the side that prevailed 1-0 at the Liberty Stadium and kept a sixth successive clean sheet in the Barclays Premier League.
"I think it was a very important win,” Clasie said. “We've been doing well the last few weeks, and we know after this game comes a short break, so we said to each other we have to win this one and then enjoy your days off this week.
“Everybody knew what our job was and we had to do it well. It was not the best game from us, but the three points was the most important thing.
"Defensively, the organisation was very good. Maybe we gave one chance away, maybe one-and-a-half, but that's max. I think that's the most important thing in football – stay defensively good and then you'll create your chances by yourself. We did that, and in the second half we scored.”