Northamptonshire 171 for 3 (Levi 57, Crook 46*) beat Essex 168 for 5 (Napier 38*, Rutherford 36) by seven wickets
Steven Crook was hailed as the "Northants Botham" after his all-round contribution helped Northamptonshire in to the final of the Friends Life t20 for the first time.
Crook thrashed an unbeaten 46 from only 24 deliveries as Northants completed the highest successful run-chase in the history of T20 Finals Day. With Cameron White he forged an unbroken fourth-wicket stand of 78 in just 35 balls, leading the captains of both sides to suggest he should be of interest to the national selectors.
"I believe England should be taking a look at Crook," Essex captain James Foster said. "He bowls with pace, he has good options and he is one of the few guys around who can strike the ball out of the park. We didn't do too much wrong today; we were just beaten by two guys who played exceptionally well."
Northamptonshire captain Alex Wakely agreed. "He can't do anything wrong at the moment," he said. "He's the Northants Botham. He has been a great singing for us and he is producing in all formats of the game."
The performance marked another step in the rehabilitation of Crook and the Northants team. Heading into this campaign, Northants, who last won a trophy in 1992, had won just three of their last 27 T20 games dating back to their quarter-final defeat in 2010 and Crook was a 30-year-old whose career had never reached the heights his talents suggested it should have done.
Indeed, not so long ago he left the game to pursue a career as a rock singer but, after struggling to make the breakthrough, ended up as the in-ground DJ at Northants in 2010 when they hosted limited-overs games. He returned to cricket with Middlesex in 2011 and 2012, but was lured back to Northants by the promise of featuring in all formats.
But now, Northants have won nine of their 12 matches this season and Crook, in his second spell at the county, is beginning to gain the attention of the England and, perhaps, Australian selectors. Born in Adelaide, recent rule changes - the "Robson Rule" as it has been dubbed - mean Crook is eligible for both.
In such form, playing with infectious confidence and joy, he will prove hard to resist. After bowling his four overs with pace, he utilised his strength to pummel four sixes and three fours. At one stage White and Crook scored 51 in 13 legitimate deliveries.
Northants were given a good start in their run chase by Richard Levi. He made 57 from 35 balls, taking 21 off David Master's third over, and posting an opening stand of 74 in 8.2 overs with Kyle Coetzer.
But when Levi mis-timed a full toss to mid-on - replays suggest it was desperately close to being a no-ball for being over waist height - it seemed the Northants innings might stall in a spell where they lost three wickets for 19 runs in four overs. But White and Crook, targeting the left-arm spin of Tim Phillips, who was hit for three sixes in five balls at one stage, revived the chase and ensured victory with 11 balls to spare.
Earlier it seemed that an explosive contribution from Graham Napier might prove the difference between the sides. Napier, coming to the crease at the end of the 16th over, thrashed 38 from 15 balls to help give Essex a total 24 higher than par on this ground this season.
In partnership with his captain, James Foster, Napier added 54 runs from the final 26 balls of the innings to transform a modest target into the largest that Northants had been asked to chase all campaign.
The defeat means that Essex have now lost in the semi-final on all four of their trips to Finals Day.
George Dobell is a senior correspondent at ESPNcricinfo