"It just wasn't our day," McNamara is quoted as saying by Sky Sports News. "The goal going in just before half time was a real body blow for us but we tried to break them down in the second half and it just wouldn't go for us.
"We had chances but there's a thin line between winning and losing sometimes and I'm disappointed with the goals, especially the first one.
"I think we can play a lot better. I think we can raise the tempo, which we tried to do more in the second half."
Dundee finished the Scottish Premiership season in fourth place in the table.