Whatever Diamond told his players at half time worked as Worcester regained the momentum in the early stages of the second half. They retook the lead when Vailanu brushed off three defenders to run in from 30 metres out.
Worcester stepped it up physically, and Bristol were temporarily reduced to 14 men when Jac Bates got sent to the sin-bin for an intentional knock-on.
The home side dominated the rest of the game to grind out a significant result.
Match details
Scoring sequence: 5-0 Van der Merwe try, 7-0 F Smith con, 12-0 A Beck try, 14-0 F Smith con, 14-5 S Luatua try, 14-7 C Sheedy con, 14-12 Lahiff try, 14-14 C Sheedy con, 19-14 S Vailanu try.
Worcester Warriors: J Shilcock; P Humphreys, A Hearle, B Searle 41), D van der Merwe; F Smith, G Simpson (W Chudley 67); M McCallum (E Waller 58), N Annett , C Judge (J Tyack 78), M Garvey (A Kitchener 58), G Kitchener (J Clegg 60), J Batley, M Kvesic, S Vailanu (I Miller 63).
Replacements: S Atkinson.
Bristol Bears: I Lloyd; J Bates, S Radradra, P O’Conor (A Frisch 53), A Leiua; C Sheedy, T Strang (T Venner 53) (H Purdy 67); Y Thomas (J Woolmore 41), J Kerr (H Thacker 47), M Lahiff (A Challenger 58), E Holmes (J Joyce 58), C Vui, S Luatua (S Jeffries 51), D Thomas, F Harding.
Sin-bin: J Bates.
Referee: Wayne Barnes.
