A last-gasp winner from Ryan Boulding allowed United to pip both the Dons and Kilmarnock to the final place before the league split, with Killie suffering defeat against Dundee.
With his side's attentions now focused towards the top of the table, McNamara is eyeing up third-placed Inverness and possible European football.
He said: "It was a great feeling to score when we did.
"We were on the end of a late goal from St Johnstone the other night and we were a bit deflated after it. This goal more than makes up for it.
"I think it was deserved, especially in the second half. I was just delighted for everybody connected with the club."
He continued: "We've had a couple of disappointments over the last couple of weeks and this makes up for it.
"This game was about winning and doing our jobs properly and we did that. Inverness are seven points ahead of us and that's the target now."
- Sports & Recreation