The Trotters went down to Pompey 1-0 at Fratton Park, leaving them in a precarious position in regards to Premier League survival and Megson was less than happy with the outcome.
"Basically we were poor and Pompey were not that much better than us, but I can't think of any of our players who did as well as they are capable of doing," he said.
"We've got to show a big improvement on this, even though three of our last five matches are at home. We are certainly not thinking we are safe yet.
"The performance was not good enough, not coming up to the standard that we've set for most of the time this season and certainly not what we need at this stage of the season.
"It's purely and simply about results and for the life of me and probably everybody else, I thought that was going to be a 0-0.
"Yet we've probably been responsible for our own downfall."