Protectionist claimed the third and most important victory of his second stint with Andreas Wohler when successful in the Grosser Preis von Berlin at Hoppegarten on Sunday.
The six-year-old won the 2014 Melbourne Cup under Ryan Moore during his first spell with the German trainer, after which he remained in Australia to be trained by Kris Lees.
However, following a largely unsuccessful year Down Under, he was sent back Wohler's stable by owners Australian Bloodstock and it has proved a shrewd decision.
Following a comeback win at Dusseldorf in June, Protectionist stepped up in class to land a Group Two at Hamburg.
He returned to Group One company for his latest assignment and struck by two and a half lengths from Nightflower under Eduardo Pedroza to secure his first victory at the highest level since his Melbourne Cup heroics.