Skipper Ronnie Irani struck a superlative unbeaten 100 to lead Essex Eagles into the quarter-finals of the Twenty20 Cup as winners of the South Division.
Irani's well-paced innings saw his side to a testing target of 174 by four wickets as Sussex Sharks' challenge ended with a third-successive defeat at Hove.
Sussex's 173 for five was their highest score in the competition in 17 matches and was built around a fluent 73 from 44 balls from opener Matt Prior.
Essex needed eight off the final over from Mike Yardy with six wickets in hand.
Irani smashed the first ball for six over backward square leg and then took a single, but Essex lost Ryan Ten Doeschate and James Foster off the fourth and fifth balls before Irani despatched the final delivery for four.
Irani finished with 13 fours and two sixes in his magnificent 61-ball innings.
Together with Mark Pettini, Irani gave Essex an ideal start by thrashing 44 off four overs before Pettini miscued an attempted drive in Robin Martin-Jenkins' first over.
Darren Gough maintained the momentum by adding 47 in six overs with his skipper, Gough falling to a smart return catch by Martin-Jenkins having fired 20 off 15 balls.
Essex needed 51 from their last six overs when Will Jefferson, after smashing Sean Heather for two successive sixes over extra cover in the previous over, was taken at backward point off Yardy.
Prior's highest score in the competition helped Sussex set a challenging target and he shared in a second-wicket stand of 73 in seven overs with captain Chris Adams after the Sharks chose to bat.
Adams (36) slammed three fours and a six over mid-wicket off spinner James Middlebrook before being pinned in front in Jahid Ahmed's first over.
Prior, who had produced a disappointing 106 runs in seven previous innings this season, powered to his 50 from only 30 balls by hoisting off-spinner Grant Flower for six over mid-wicket.
Sussex lost Luke Wright when he skied a delivery from Ravinder Bopara to long leg, and Prior's entertaining knock ended when he attempted to reverse sweep a delivery from Gough and was bowled.
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