FRIENDS PROVIDENT t20, Chelmsford:
Sussex 174-5 (20 ovs) beat Essex 157-9 (20 ovs) by 17 runs
Prior's quick 50 contained four sixes and four boundaries
South Group leaders Sussex grabbed their first FP t20 win in three matches despite a 90-run stand from Essex pair Mark Pettini and Jaik Mickleburgh.
The visitors had reached 174-5 in their innings with Matt Prior leading the way with a half-century.
Essex looked to be in control after openers Pettini (59) and Mickleburgh (32) reached 90-0 within 11 overs.
But they then collapsed, losing 9-49, including three run outs, as they ended on 157-9, losing by 17 runs.
Essex went into the match in confident form, having won their last five FP t20 matches.
But Prior's contribution for the visitors, an innings in which he hit 50 off just 27 balls, proved crucial as Sussex claimed victory.