Don't know of any who sucked to start, but that kind of thing rarely gets included in a history.

Jacques Anquetil had a pretty bad day once. I forget the race (I'm sometimes horrid on names). It was a two man time trial and very prestigeous. He was teamed with Rudi Altig and by the end could barely hold Rudi's wheel, even though Rudi had been doing most of the work up front all day. To top off the day the finish was in a stadium and it was entered by a tunnel. Anquetil was so tired he did not make the turn and crashed into the wall.

The good news was that the times were taken at a point before the stadium entrance and Rudi was having a great day and his basically solo effort was enough to win.

Unlike boyhood slow starts this one is recorded because some (myself included) think the mark of a champion is being able to keep trying when things are going wrong, to keep pushing when you are there seems no hope.