The visitors led for almost 80 minutes thanks to David Connolly’s razor-sharp instincts in front of goal.
But just as at Bristol Rovers a fortnight earlier, United were forced backwards in the closing stages and were pegged back for a 1-1 draw.
Robbie Threlfall was adjudged to have forced the ball over the line after the visitors failed to clear a 91st-minute corner.
It was a big blow to Lewis, whose side dropped out of the top three as a result.
“I’ll be honest, I’m fuming. I’m not happy at all,” he said.
“I think we should have come away with three points, definitely.
“We were a goal ahead and I just thought in the last 20 minutes we didn’t impose ourselves on the game.
“We should’ve done better going forward, we had good possession and we gave it away too cheaply.”
He added: “We didn’t win enough headers or enough tackles in the last 20 minutes.
“I was fairly happy up to that point. I always felt we could go and get another goal, especially as the game went on because Morecambe were going to press even more for an equaliser.
“We just seemed to put ourselves on the back foot with some bad decisions.”
Not for the first time in his four weeks in charge, Lewis’ teamsheet revealed some surprises.
Midfielder Scott Davies was given the task of replacing the suspended Tom Newey at left back.
It was part of a back four which saw Sam Long handed his senior debut at centre half, while right back Matt Bevans was given a rest.
Lewis said: “Matt Bevans has been really good, but he’s a young kid who has played six games on the trot and sometimes youngsters need a breather.
“We didn’t think young David (Lynn) was quite ready yet, although he’s improving.
“I thought Scotty did a decent enough job at left back and Sam Long was excellent on his (full) debut.”
With seven first-team players unavailable a draw was not a disaster, although Lewis thought it would take until today to draw some positives from the result.
He said: “Probably come Monday morning I will do, but at the moment, no.”
Deane Smalley and Dave Kitson both missed the game with minor hamstring injuries, but Lewis hopes the pair will be available for Saturday’s visit to Rochdale.