Didn't realize you were there, sorry not to see you!
I too had a surprisingly long time for the final km.....I am pretty sure the 9km marker was early (and in fact that the km markers in general were not that accurate). My pace/position didn't change much in the final km vs people around me, pretty sure there was no dramatic slowdown!
Makes sense ... of course this means that my previous km must have been slower than I thought!