Darren Maddy hit a superb 48-ball 84 to the Foxes into the Twenty20 Cup semi-finals at the Eagles expense.
Unfancied Leicestershire advanced to the semi-finals of the Twenty20 Cup for the second year after Darren Maddy again demonstrated his talent for scoring rapid runs under pressure to set up a 14-run victory over Essex here.
Maddy's brilliant 84 off 48 balls helped Leicestershire to reach 180 for 6, and although Essex finished closer than they might after an intelligent and productive partnership between Grant Flower and Paul Grayson, the target ultimately proved just beyond them.
Ousted from the Cheltenham & Gloucester Trophy by Devon in one of the season's bigger shocks, Leicestershire have made little impact in either the Championship or National League after last season's double relegation. Yet they have discovered the knack of winning games in this format and Maddy in particular has excelled.
Yesterday's flurry of strokes, a thrilling combination of classic and improvised, took the former England right-hander's aggregate in this season's Twenty20 to 262 from five innings, including a century and two 50s, which outscores more celebrated big-hitters such as Graeme Hick and Andy Bichel.
The brief window between the zonal games and the quarter-finals had left Leicestershire with insufficient time to prepare a fresh wicket. Last night's track was getting its third use in nine days and was certainly not ideal for the high-scoring tempo the crowds most like to see.
But it proved little handicap to Maddy and his captain, Brad Hodge, who put local knowledge to the best use in putting on 83 for the first wicket before Graham Napier found a way through the Australian Hodge's defences. Darren Stevens then produced an equally valuable supporting role before Maddy, who hit three sixes and a dozen fours, skied a ball from Ravinder Bopara which the wicketkeeper, James Foster, caught almost at midwicket.
Ottis Gibson became the first of two victims for Darren Gough and Stevens fell to Andre Adams, the New Zealand all-rounder who joined the county only last Saturday, but by then Leicestershire had gone past what they had expected to be a "par" score and their final total posed Essex a challenge that looked particularly stiff.
It was an unfortunate night for Ronnie Irani, the Essex captain, who took the decision to field first even though Leicestershire's record in chasing totals is poor. To double his discomfort, he was caught at midwicket off the first ball of his side's reply.
Mark Cleary, celebrating his 25th birthday, struck for a second time with the last ball of an eventful first over when Napier, whose straight six off the fourth ball earned a year's supply of beer for a "fielder" in the crowd, was caught at cover.
Cleary's direct hit from midwicket ran out Adams as Essex slumped to 33 for 3. Grayson and Flower hit half-centuries, off 34 and 45 balls respectively, in a stand of 95 for the fourth wicket, but they were both dismissed by Gibson in the 18th over, with 48 still to get, after which the result was never in serious doubt.