Well as the problem was just to return only one winner, I just evicted duplicates, which doesn't allow the other problem where you would want to return an ordered list of "winners" (?)
If that was the case, I would obviously choose another method to keep my results ordered (maybe an OrderedDict like you did)

Sorry, I debuged with your source code.
I realized setdefault is only one saved in dictionary.
Yes. the other problem is exists.
Original problem: return first player
The other problem: return first, second player

How about?
In case

print(winner([c16, c17, c18])) #Rob, Gandalf
print(winner([c18, c17, c16])) #Gandalf, Rob

scores only store the first candidate for each total score when iterating candidates, which is ordered, and so the order is "preserved" as I evict all duplicates (look at the setdefault method usage)

Maybe I shouldn't have used a dictionnary for this and just stored a winner variable updated when seeing a candidate with a better score, this would have been easier to read I think.

How about equal player??
dictionary is not ordered.
scores is dictionary that not ordered.