And they triumphed despite having to play most of the second half with only 10 men after skipper Garry Moody was sent off for a foul on Ben Anderson.
Six of the goals were shoehorned into the first 45 minutes - Fareham leading 4-2 at the interval thanks to Curt Robbins, Josh Benfield and Jack Breed (2).
Sam Hookey had levelled for the Deans, who had won 12 and drawn twice since their only previous Wessex Premier loss of the season, 1-0 at Hythe on September 3. Connor Duffin also replied just before half-time.
Though having a numerical advantage, the Deans had to wait until late on in the second period before Harry Jackson completed the scoring.
5. Fareham score one of their four first half goals
Fareham score one of their four first half goals. Picture: Keith Woodland Photo: -
7. Horndean's Zack Willett on the attack
Horndean's Zack Willett on the attack. Picture: Keith Woodland Photo: -
8. Horndean's Robbie Taw (white) goes up for a header.
Horndean's Robbie Taw (white) goes up for a header. Picture: Keith Woodland Photo: -