Sussex 199 for 9 (Yardy 61, Wright 3-43) beat Warwickshire 182 (Beer 3-27, Nash 3-27) by 17 runs
Sussex moved into pole position to qualify for the CB40 semi-finals after leapfrogging Warwickshire at the top of Group C following a 17-run victory.
The third-placed Bears were dismissed for 182 in the final over replying to a modest 199 for 9 to leave Sussex needing to beat Yorkshire and Kent to secure their place in the last four. Warwickshire and Kent, however, can still go through if the leaders slip up.
Sussex's spinners were the key to victory; they bowled 21 overs between them on a slow pitch. Mike Yardy set the tone by conceding just 23 runs in his eight overs, before leg spinner Will Beer took centre stage, claiming 3 for 27.
Having run out Will Porterfield, Beer starred after being brought into the attack by having Tim Ambrose caught behind and Jim Troughton stumped. He completed his haul when he bowled Darren Maddy off an inside edge.
Offspinner Chris Nash had the dangerous Rikki Clarke caught at extra cover and returned in the 38th over to end a threatening 52-run stand between Keith Barker and Steffan Piolet by bowling the former as he tried to clear the leg-side boundary.
That left Warwickshire needing 34 off the last three overs, and Nash secured victory in the last when he castled Chris Wright to also finish with 3 for 27.
Earlier, Sussex had been indebted to Yardy, who made the only half-century of the match.
Wright took three wickets in nine balls - including that of namesake Luke for a golden duck - to reduce Sussex to 34 for 3 in the seventh over. Yardy and Murray Goodwin then put on 62, only for the latter to play on to Jeetan Patel's quicker ball for 36; Patel also picked up Joe Gatting to finish with 2 for 29.
At 125 for 6 in the 27th over, Sussex were in trouble. But Kirk Wernars counter-attacked before Yardy chipped a catch to mid-on, having hit five fours in his 61. Wernars finished unbeaten on 37 and a target of 200 proved beyond a Warwickshire side whose hopes of reaching the last four may have been fatally damaged by two defeats in the space of 48 hours.