Čilić, playing his third final on the bounce, beat former champion Kevin Anderson 7-6(6), 6-7(7), 6-4 in three hours and eight minutes to win the Delray Beach Open by The Venetian Las Vegas title.
Čilić, who now has 11 career titles, is coached by the former Wimbledon champion.
“It wasn’t easy for my nerves, for Goran’s nerves especially,” said Marin after the final, before adding “In the final some nerves can get into your body and you have to deal with it in the end. Luckily I found a way.”
Čilić has now won an impressive 18 matches in 2014.