I believe a veteran David Ferrer is being underestimated here. Surely, at the age of 36 he is not what he used to be and cant rely on strength and quickness anymore so he dropped massively on the ranking. It was especially hard for him on clay and grass but when we look at hard court results from this season we can see that his losses were expected as he played really strong opponents. His last four hard court tournaments were Rotterdam, Acapulco, Indian Wells and Miami and he lost twice to Alexander Zverev and twice to Delpotro where in 3 out of those 4 matches he put up a really good resistance. Klahn on the other side is a 100+ ranked player without much of an experience so i can see Ferrer winning here.