I would further suggest that contest entries should be sorted by newest entries first — the reason being that every entrant would have exactly one chance to sit in that "top spot" until sorted down by newer entries.
Further, for anyone following the latest 'activity' (to vote), folks would no longer have to crawl through all the entries again and again looking for those latest entries since my last visit. As the number of posts grows, finding what's new gets more difficult — so folks are less likely to bother. Putting the newest entries at the top helps mitigate that.
You can't (easily) nullify the fact that early entries simply have more time (and short-tail attention) to accumulate more votes, but letting the newest entries trickle down from the top will help offset the advantage of simply being here first (if even just a bit).
Oh, and then change it back to "top winners first" when the contest is over.