The London club were cruising with a 6-2 advantage at one point but Hucknall levelled at 7-7 midway through the third period. Hucknall eventually took the lead for the first time at 10-9 and went to 12-10 early in the final quarter - but it wasn't enough.
Two goals by Denes Csizsinszky made it 12-12 before Tilemachos Pissas hit the winner just 43 seconds from the end.
The Portobello-City of Bristol clash produced an equally tense finale. Goals by Andrew Melville and Chris Raffo eased the Scots from 6-6 to 8-6 in the final period only for Bristol to grab a point at 8-8 with goals by Stuart Fennell and - with 16 seconds remaining - Nathan Brown.
Manchester Hawks' 15-12 victory over Cheltenham Spartans featured hat-tricks by Conor Lynch, Adam Lecomber and Dan Bentham. George Wood scored five for Worthing, who beat Castleford 12-6.
Photo (Trevor Hyde): Tilemachos Pissas scores for Otter against Hucknall today.