The game was tied at 8-8 until Matt Elliott edged Coventry ahead with 2.41 to go. Sam Greenhill added a final Coventry goal just 26 seconds from the end.
Invicta Marlins and Watford Saxons were the only teams to win twice at Walsall. Newcomers Sedgefield lost 12-7 to Chester on day one but bounced back with a 15-4 victory against Cambridge.