While relegated, the result is significant as it takes Saints to 12 points and so surpassing Derby County's worst ever Premier League points tally of 11.
Rusk said afterwards, "We're feeling obviously good. We knew the size of the task today. I think for me, it was more about the principle of what today was.
"We knew there were going to be some challenges ahead of us, even over the seven games. There was a lot of pressure involved with that, and I think today we handled that really well.
"It's not for me to focus on the external voices or about people writing us off or having their opinion.
"My job is to stay measured and somewhere in the middle, and that's the best way of supporting the players in this situation.
"So, yeah, we had our game plan. We wanted to build on all the things we've done really well over the last four games - apart from last Saturday."
Delighted for fans
Rusk also said: "We were disappointed with last Saturday, but as I mentioned the other day, I think our priority was to become a harder team to beat on day one of my tenure.
"We were definitely making great strides towards that. I think today we were a little bit more complete from that point of view.
"I'm delighted for the players, delighted for the supporters today. It was a nice moment when the referee blew his whistle at the end."
Beating Derby points mark
On reaching the 12 points mark, Rusk admits he was aware of the significance of outdoing Derby.
He continued, "I didn't know much about the points record, did I? I wasn't making it my main focus. I was well aware of the significance of the points record.
"I totally understand how important it was for the club to fight to not have that. But for me, it was about focusing on how I could improve the team.
"How do we get the best performances possible? How can we give the supporters something to identify with in a short space of time?
"And I felt if we'd done those things and done them to the best of our ability, that we would get the points required.
"We nearly got a great point against Fulham. We nearly won away at West Ham, and today, in my opinion, we've got what we deserved out of the game.
"So, I was confident that we could get past the points record, but I think it was about staying measured, really, and just focusing on performances."