The winger fittingly bagged on his 300th league game, striking home the Eagles' opener just minutes after kick-off.
He said: "Moments like that [scoring], when I do retire, I'll obviously cherish. It means nothing if you lose on one of those milestones but to cap it with a goal and a very impressive victory at Old Trafford is one I'll remember for a very long time.
"We know we've got quality in the squad. We showed it at times last season. This season we have one or two young players, as you saw when Ebs [Eberechi Eze] came on at the end, we added that.
"We're fully confident, we knew it was United's first game and maybe we could catch them cold. We did that in the first five minutes. Once we get ahead we know we're a very well-drilled team and we knew we had enough in the dressing room to see out the result today and we more than did that."
Townsend added: "Mentally we knew we had an advantage. Whether that meant something or it was just in our minds, we knew if we started fast we might catch them cold and we certainly did that. It was just about seeing out the game plan."