Larkin, who had fringe roles at the Dallas Mavericks, New York Knicks and Brooklyn Nets, scored 30 points to go with seven assists and as many rebounds, while Serbian guard Vasilije Micic added 25 points.
Anadolu Efes scored 14 three-pointers and dominated the boards as they collected 41 rebounds to Fenerbahce's 21, carving out a 45-40 halftime lead after their rivals had nosed ahead 20-19 at the end of the first quarter.
Livewire Larkin scored the opening seven points for his team in the second half and although Fenerbahce briefly cut the gap to 57-53, Anadolu Efes pulled away to 64-55 shortly afterwards and never looked back.
Czech centre Jan Vesely netted 14 points for Fenerbahce and Erick Green added 13, but the 2017 champions fell short as they sorely missed injured Italian forward Luigi Datome, with their backcourt misfiring throughout.
Holders Real Madrid, the winners of a record 10 titles in Europe's premier club basketball competition, clash with fellow heavyweights CSKA Moscow (seven titles) in the other semi-final later on Friday.
(Writing by Zoran Milosavljevic; Editing by Toby Davis)