Sheikh Ahmed's son of Elusive City has won at Warwick, Haydock and Doncaster already this season before finishing third at Salisbury last time out.
Reunited with jockey Andrea Atzeni, Kohlaan returned to winning ways, making every yard of the running to win by two and a half lengths.
Andrea set a decent tempo early on but was able to get a 'breather' into Kohlaan at the top of the straight. He picked up well with two furlongs to run and was never headed.
Roger said: "Kohlaan is not the most straightforward at home but Andrea gets on really well with him and he has galloped them into the ground."
Kohlaan on Warren Hill under his regular rider at home Petr Kriz