The Swiss icon shot past Youzhny 6-3, 6-4 in the grass-court Wimbledon tuneup event, improving to 15-0 all-time against the Russian.
Federer, who will be seeking to defend his Wimbledon crown later this month, ran his all-time grass-court record to 121-17 with Sunday's victory.
Federer previously won the Gerry Weber event in 2003-06 and in 2008.
Youzhny fell to 8-11 all-time in finals.
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