Cilic has won both their previous meetings. The most recent was in May 2015. he won at the French Open on clay in straight sets. Both their matches were on clay.
You’d expect Mayer to be the stronger clay player so now they’re on Cilic’s best surface I don’t rate the Argentine’s chances. Mayer has been pretty poor this season but he has improved in this tournament with wins over Groth and Troicki.
Cilic had a decent Australian Open with a third round finish. He lost to Harrison in Acapulco but got some revenge over the American when they met in this tournament.
I have to favour Cilic on this surface but I think we will see him trade a fair bit higher than 1.38 . Back Cilic above 1.60