The win will see Thornbury not only end the season as champions of Berkeley Division 2 but also see the team promoted for the second successive season.
The team still have two games to play; away at Wotton 2s on Saturday and then a rearranged game against Hanham on April 1.
Thornbury took the lead after just four minutes when Jess Mundy scored the first of her two goals and Coz Deas soon followed with another well-crafted effort whilst Ella Clark and Vicky Ball both scored with efforts that gave the keeper no chance.
At one stage, Thornbury sat back on their three-goal lead but a goal from the visitors made Jo Deas side return to their usual attacking style and two further goals extended the home lead.
As for the Thornbury 2s, they were comfortable 4-0 winners against Wotton 3s in an entertaining game.
The Thornbury goals came from Claire Brealey, Amelia Fitzgerald, Sarah Lally and Emily Board. Lauren Lever on a rare excursion from defence narrowly missed joining the scorers when her shot was well saved by the Wotton keeper.
David Anderson scored the only goal for Thornbury men in a 5-1 loss at Old Bristolians