Before the start, both teams were stranded at the bottom of the table without a point - but with Sheffield holding a key advantage of superior goal difference.
Otter led for much of the game, although Sharks battled with great determination to draw level after trailing 5-3, then 10-7. Briefly, Sheffield led 11-10 at the start of the last - a goal by Anna Motley (Photo: Trevor Hyde) after Otter had a player excluded. But Otter were soon ahead again, as Niamh Moloney equalised and Rebecca Mulcahy, Emily Campbell-Lamerton and Isabelle Dean established a 14-11 lead. Sheffield's final goals were not scored until the last 50 seconds and so Otter claimed the points.
Sarah Snyder (4), Isabelle Dean (3) and Rebecca Mulcahy (3) were the main Otter scorers while Rosie Griffiths and Larissa Partridge claimed hat-tricks for Sheffield.
In their second game, Otter went down 20-13 to Liverpool Lizards, who take on Manchester tomorrow in a title decider. Manchester defeated Coventry 22-6.