The Brumbies, who went into the game without injured skipper Stirling Mortlock, led 18-0 at half-time after tries from utility back Julian Huxley and lock Adam Wallace-Harrison.
The two-time Super rugby champions then produced an amazing steely defensive effort in the second period to restrict the top-of-the-table Sharks to just 10 points for a crucial 21-10 win in week eight of the competition.
"Stephen made some excellent decisions, some smart kicks and good organisation," Fisher said after the match.
"I was really pleased to see Stephen off the back of a month off play like that. It's fantastic for his confidence which will help the team grow."
The unexpected win has revived the Brumbies 2007 Super 14 campaign after losing two of their last three matches to South African teams, the Bulls and Cheetahs.
It also signalled a return to the Brumbies trademark attacking style of play after struggling to score in the first seven games, and to this end Fisher said Larkham's controlling presence was pivotal.
Additionally, it was the first win for the Brumbies at Durban in Super rugby history, ending a 12-year hoodoo and sees them leap back into the top half of the Super 14 table and keeps them in touch with the leading teams.
The CA Brumbies have defied the odds and a 12-year hoodoo to hand the top-of-the-table Sharks their first loss of the season in Durban on Sunday night.
The Brumbies play the last match of their three-match South African tour against the Lions at Ellis Park, Johannesburg next Saturday night.