Jim Bentley acknowledged his side were punished for individual errors by league leaders Oxford on Saturday.
The Shrimps found themselves 3-0 down at half-time and despite improving in the second period, now have only one win from their last six League 2 games.
Bentley said: “We talked all week about how we wanted to play and I thought the start was okay and we played some decent football, kept the ball well and had a decent chance through Kevin Ellison.
“But then after that we gave a foul away in the final third and didn’t defend the first phase of the free-kick well enough and it popped out to (James) Constable who’s put it in.
“Those things happen. When it’s going for you, it goes for you and when it’s not, you get punished for it.
“We’re playing against really good players at his level and we made, certainly with the second and third goals, a couple of individual errors in key areas that they’ve exploited.
“Sometimes you need the rub of the green or that lucky bounce, we had it when we went nine games unbeaten, and now we’re struggling for a bit of form and confidence they seem to be going against us and we’re getting punished for our mistakes.”
The Shrimps did have chances in the second period, including Jack Sampson hitting a post, but the visitors couldn’t snatch a goal that would have given the hope of a surprise comeback.
Bentley said: “We probably had the best chance in the first half before they scored through Kevin Ellison and had plenty of chances in the second half.
“We came here with a gameplan, we tried to play, maybe that was me being a little naive thinking we could come to top of the league, play our stuff and create chances.
“They’re a big club at this level and punished us for our mistakes. You always hope you can do another Chesterfield but that’s once in every blue moon.”