Goals either side of half-time from Sam Clucas and Jamie McGuire and a 72nd-minute effort from substitute Matt Rhead saw the Stags stroll to victory.
Burnett said: "They were better than us. In the first half we limited them to one or two chances and the crowd were even starting to get on their backs.
"Then they scored a goal and, it's an old cliche, but it changed the complexion of the game.
"We had large parts of the game without creating too many goalscoring opportunities.
"We came out sluggish for the second half and they scored again. I don't know if it was a wonder goal or a mistake, but I think my keeper might have expected to do better.
"Then they scored again from bad defending by us and it was all over. We huffed and puffed without really creating anything and we could still be out there playing now and still not score.
"We have not started the season badly. But if you are going to be successful you have to come to places and maybe pick up a point. I have no complaints about the result at all.
"We knew Mansfield would be competitive and get balls into our box and, fair play to them, they did what they set out to do."
- Sports & Recreation
- Ice Hockey
- Sam Clucas
- Jamie McGuire