"You tend to get locked up in the moment and the moment today was a Six Nations game between Ireland and Scotland," he said.
"I've always alluded to the fact that the Six Nations is about momentum. And I think we've built momentum. We haven't got the three results - we've got two out of three - but we're building momentum.
"The key now is to keep it going. That was the context of today and I felt Scotland were a team coming to Dublin with nothing to lose and everything to prove.
"I know the game didn't go their way in the end but I thought they played some really good rugby early in the game.
"They tested us like we expected to be tested. If we hadn't talked about it and prepared mentally during the week for that test, I think we could have been in trouble for long periods in the first half.
"I'm very happy that we managed the whole dynamics of the team and built on what we talked about in Paris, which was what I thought was a good 80 minutes despite some mistakes that cost us dearly in that game.
"Today was another step forward and I think that's a reasonable assessment of it."
Ireland may have outscored the visitors by five tries to one, but O'Sullivan surmised that it was really the defensive platform, pressed into action early on, that laid the foundations for the win.
"We worked very hard this week on a couple of things. One was - which was the way it transpired in the first quarter - when we spent a lot of time without the football and we had to really work our socks off to contain Scotland (who kept it through many phases).
"You don't often go into the game expecting to have to play without the ball for so long but that's the way it turned out.
"We talked about that during the week. We felt Scotland were going to play a little bit of a different game from before, and we may have to spend long periods working and working to get the ball back," he explained.
"They key was that we got one chance off that pressure and David Wallace scored off the set piece. It kind of repays all of the hard work you've done on the defensive side of the football.
O'Sullivan agreed that there is plenty for his players to work on ahead of their next game at home to Wales, although the glut of tries did give him encouragement for the remainder of the championship.
"We were more clinical today. It wasn't a perfect performance, there were a couple of things here and there that you could complain about. But I suppose five tries in a Six Nations match - you've got to be a bit upbeat about that."