Derbyshire 170 for 4 (Durston 51, Rutherford 47) beat Lancashire 167 for 9 (Petersen 79, Neesham 4-35) by six wickets
The Derbyshire Falcons kept their slim hopes of reaching the T20 Blast quarter-finals alive with a six wicket victory at Derby that dealt a severe blow to Lancashire Lightning's chances of making the last eight.
A superb 79 from 49 balls by Alviro Petersen should have taken Lancashire to a formidable total but they lost five wickets in the last two overs to end on 167 for 9 with Jimmy Neesham taking a T20 career-best 4 for 35.
Hamish Rutherford smashed 47 from 27 balls as 75 came from the first six overs and skipper Wes Durston plundered 51 including four sixes from 34 balls as the Falcons reached 170 for 4 with eight balls to spare.
Durston described the game as "do or die" for his side but Petersen and Luis Reece gave Lancashire an excellent start by taking 63 from the Powerplay.
Reece pulled and cut Andy Carter for three fours from the second over before Petersen pulled Wayne Madsen over the midwicket boundary and drove Neesham for six.
Reece scooped Carter over fine leg for another maximum but the Falcons regained some control through the legspin of Matt Critchley who had Reece lbw sweeping for 32 off 22 balls and trapped Karl Brown in front in his second over.
Petersen launched him over wide long on for six and Liam Livingstone pulled Alex Hughes over the square leg boundary but was caught behind trying to do the same to Neesham.
The South African was the danger man and he used his feet well to twice drive Carter for four but the fast bowler took an athletic diving catch at backward square leg to remove him and his departure saw Lancashire implode.
The lower order disintegrated in the last two overs with only eight runs scored as Neesham preyed on mounting panic to take three wickets and drag Derbyshire back into a game that was running away from them.
Derbyshire had fallen agonisingly short chasing an almost identical target on Sunday but after Durston top-edged a square cut for six over backward point off Jordan Clark, Rutherford unleashed some crunching drives as Derbyshire raced to 50 in four overs.
Durston hammered George Edwards over long on for another six and at the end of the Powerplay, Derbyshire were in control but Rutherford sliced a drive at Stephen Parry's second ball and was caught at backward point.
Lancashire's hopes of building on that were dashed in the ninth over which cost 16 as Parry was twice driven for six by Durston and Chesney Hughes and Derbyshire had the game in their grasp at the halfway stage with only 65 needed.
Durston completed his 50 by driving Croft over long-on and although Croft struck with consecutive balls and Neil Broom went cheaply in the 18th over, Lancashire were left to rue those last two madcap overs.