Making his debut on loan from Lincoln City, the unfortunate keeper made an April Fool Day's blunder to hand Morecambe a goal in the 54th minute which looked like being the winner in a match marred by a strong wind.
It looked like a simple collection at the near post when Danny Carlton fired the ball in from wide on the left but somehow Duffy managed to push the tame shot inside his near post.
Cambridge were struggling at that stage of the match but they were stirred into action in the 70th minute when frustrated manager Rob Newman made a double substitution.
It had the desired effect of shaking up his side, and a minute later creating the chance which Smith took superbly with a blaster of a shot from the edge of the box to equalise.
It was Cambridge that scored first with a wind-assisted effort from Jon Brady midway through the first half. What looked like a cross from his free-kick dropped over a bunch of players near the far post and simply bounced over the goal-line.
But the lead lasted barely 60 seconds as Carlton ran on to a cross from Michael Howard to take advantage of poor marking and flick the ball into the net.
Despite losing the lead and their way in the final quarter of the game it was a much needed point for Morecambe, boosting their play-off chances by ending their four-match losing run away from home.
As far as Cambridge were concerned it left them undefeated at the Abbey Stadium since November, but it was generally a muted display by a side showing five changes from their last match.
Their lack of power and penetration up front was highlighted by the fact that it took them 67 minutes to force their first corner kick in front of their home supporters.