People you wouldn't think can come last (almost) do.
I had a dreadful marathon in Rotterdam, well up the field halfway, then had to walk more or less the remainder ... made the cut-off by 8 minutes. There really weren't very many behind me at all, and the organisers were getting ready to wind it all up.
Similarly I beat someone in a 5K who should have been miles ahead of me, he came second I think at the Roding Valley Half in 2004, but got an almighty stitch. Although he was nowhere near last, sometimes unexpected things happen!