The Londoners fell a goal behind with just 95 seconds on the clock as David Silva slotted the ball into the net from close range.
The same player added a second for City after the restart, but Briggs believes that the damage was done during the opening two minutes of the encounter.
"The Etihad Stadium is one of the toughest grounds to visit," Briggs told the club's official website. "So when you concede so quickly, it makes it even harder. There are few teams that would recover from that, and of course, it set us back.
"You don't want to be chasing a team like City for so long, on top of that, they don't give much away here either. They are the champions of England and have so many world-class players.
"In a football sense, coming from behind at City is one of the biggest challenges. It was an uphill battle, and it just didn't happen for us. You never want to go behind so early on, and this was an example of that."
The loss has seen Fulham drop to 14th in the Premier League table.