The London side led from the start - 3-1 in the first period, then 4-3 at the halfway stage. It would have been worse for Manchester but for two penalty saves by their goalkeeper Sophie Jackson.
Lucy Bullock's goal from distance put Otter 5-4 up early in the third period and two more goals by Bullock made it 7-4. That's how it stayed for much of the final quarter, in which Manchester had their chances - only to be either thwarted by goalkeeper Molly Dilalla or spoil promising attacks with indifferent finishing.
Earlier, Liverpool Lizards beat Hucknall 13-9 to take third place. Milly Wordley led their scoring with five.