The son of Oasis Dream was starting out in handicaps off a mark of 65 and he duly obliged under a well-timed ride by Andrea Atzeni.
Settled in the midfield, Andretti travelled well throughout the contest before making his challenge up the straight.
He took a while to overcome the leaders, getting up in the shadows of the post to win by a neck.
Roger said: "Andrea has given him a good ride. He has improved with every run and looks as though he will stay a mile."