Sussex 216 for 7 (Philippe 70) beat Somerset 169 (Rossouw 74, McCoy 5-33, Mills 4-32) by 47 runs
Rilee Rossouw's blistering 74 from just 29 balls failed to save Somerset from their first Vitality Blast defeat of the season as Sussex Sharks enjoyed a 47-run success at Taunton.
The visitors posted 216 for seven after losing the toss, Josh Philippe leading the way with 70 off 43 deliveries, Ravi Bopara making 48 and Harrison Ward blitzing 23 off five balls at the end.
It didn't look like proving enough as Rossouw took his tally of runs in four Blast innings for Somerset to 248, at an average of 82.6, with his most devastating display to date.
The South African left-hander blasted five sixes and eight fours. But he lacked any meaningful support and a dramatic late collapse to 169 all out saw Obed McCoy finish with five for 33 and Tymal Mills four for 32 to help Sussex claim their second win in four games.
An almost white pitch looked full of runs. But Somerset went into the game full of confidence and Tom Lammonby initially maintained their momentum by bowling a maiden to Philippe.
Luke Wright began by hitting his first two balls from Josh Davey for four and six, but perished in the same over, was caught at cover off a wide one.
Philippe and Tom Alsop then produced a battery of sixes to take the total to 62 by the end of the six-over powerplay before Alsop fell for 30 to the left-arm spin of Roelof van der Merwe.
Bopara used his experience to score quickly without taking risks as he and the increasingly effective Philippe added 85 in 9.3 overs.
The Aussie went to a 35-ball fifty in the 14th over, while Bopara survived a caught-and-bowled chance to de Lange before falling to Davey in the next over.
After launching Ben Green for successive sixes, Philippe chanced his arm once too often and was caught backward point.
Delroy Rawlins and George Garton cleared the ropes to boost the Sharks' total, but both fell and the visitors were still eight short of 200 when de Lange began the final over.
Having dismissed McCoy lbw with a full toss, the powerful seamer proved no match for 22-year-old Ward, who survived a run out opportunity to wicketkeeper Tom Banton taking a scampered bye before transforming the Sussex total.
He smashed de Lange for 6,6,4,6 off the final four balls of the innings to give the Sharks a spring in their step when they came back out to field.
Will Smeed fell cheaply to McCoy, skying a catch to deep square in the second over after Garton had conceded only a single from the first.
But Rossouw was soon into his stride, taking ten off his first three balls from McCoy and following up with two sixes and a four off the fourth over, sent down by Mills.
Banton's early run of low scores in the Blast continued when he was caught and bowled by McCoy attempting a scoop shot.
But Rossouw's assault was relentless as he charged to a 17-ball half-century with a pulled six off Steve Finn, helping Somerset to 64 for two at the end of the powerplay.
Three more crunching boundaries followed in the next over from leg-spinner Archie Lenham. By the end of the eighth Rossouw had scored 73 of Somerset's 90 runs.
When he was out to a top-edged sweep off Rawlins, the home side's run-rate dropped and Tom Abell's departure for 23 in the 13th over left them requiring 97 off 46 balls.
Somerset never recovered. Bopara conceded only five off the 15th over and a series of increasingly desperate shots saw McCoy and Mills run riot in the closing overs as the last six wickets fell for 17 runs.
