3 neutral positions:
24/2006 ATP London (GBR) Grass Lleyton Hewitt Rafael Nadal 3-6 6-3 ret. 1/4
30/2006 ATP Umag (CRO) Clay Stanislas Wawrinka Novak Djokovic 6-6 ret. Final
40/2005 ATP Metz (FRA) I_Hard Yuriy Schukin Novak Djokovic 4-6 6-4 ret. q-Second
for the first and the thrid you could say that the momentum was against them when they retired.
Splitting the first two sets with the exact same scoreline isn't something that would rattle any professional player, unless he's up against a top seed who's the heavy favorite for the deciding set. I don't think that was the case for either the first or the third match.
As for the second match, it wasn't exactly a neutral position scorewise (i.e. equal games/sets or on serve). Djokovic was up 3-1 in the tiebreak when he retired, so he was definitey closer to a one set lead than his opponent.