The third-placed hosts ran in seven tries on their way to recording a whitewash 39-0 triumph over the league leaders to end the campaign in some style.
Lydia Cronin and Steph Wyatt (both two) along with Amy Brittan, Kirstie Hopkins and Mary Jane Pierre were Havant's scorers.
Portsmouth Valkyries now face an anxious wait to see if they are crowned champions with Crawley Ladies hosting Farnham in their final fixture of the season this weekend currently sitting three points off the table-toppers in second spot.
n Havant Ladies' first XV ran out 65-7 victors over Oxford Harlequins Women in their NC 1 South West (west) clash at Hooks Lane.
With their final game of the season to come at Cheltenham Ladies 2nds this weekend, they are guaranteed a third-placed finish in the division.
1. Havant Ladies Sirens player Amy Brittan holds off an opponent
Picture: Dave Haines Photo: Dave Haines 07708 405508
2. Havant Ladies Sirens' Kirstie Hopkins embarks on a run forward
Picture: Dave Haines Photo: Dave Haines 07708 405508
3. Rebecca Vaughan stays strong for Havant Ladies Sirens
Picture: Dave Haines Photo: Dave Haines 07708 405508
4. Emi Sutton firing over a conversion in Havant Ladies' win over Oxford Harlequins Women
Picture: Dave Haines Photo: Dave Haines 07708 405508