It took the hosts just three minutes to take the lead as Aled Thomas crossed for the game's opening try, and his side got another 10 minutes later when the referee awarded a penalty try after Ospreys collapsed a maul.
The Welsh side were gifted a route back into the match when a poor Gloucester pass was intercepted by Ben John, who raced the length of the field to score.
However, Gloucester extended their lead on the stroke of half time when Billy Thornley scored his first senior try.
Fussell atoned for his his error in the 60th minute to bring Ospreys back into contention, and Tom Grabham set up a dramatic finish when crossed for their third try of the game with only a few minutes left.
They could not snatch the win, though, as Gloucester remained firm in the final few phases of play.