Durham 157 for 5 (Lees 67*) beat Lancashire 83 (Potts 3-8) by 74 runs
Durham maintained their Vitality Blast quarter-final hopes with a fourth straight North Group win - by 74 runs - as Lancashire crumbled in pursuit of 158 on a used pitch at Emirates Old Trafford.
Alex Lees top-scored with an unbeaten 67 in Durham's 152 for five, boosted to 157 with five penalty runs for foul and abusive language - thought to come from Liam Livingstone after being dismissed in the home chase.
Matty Potts struck three times in a brilliant second over of Lancashire's innings as the hosts slipped to 9 for 4 and never recovered, being bowled out for their record low total of 83 in 15 overs.
Potts finished with a career best 3 for 8 from three overs.
While they still remain second in the North on 12 points and are already quarter-final bound, Lancashire's chances of a home tie have been hit with this heavy defeat in their 200th T20 fixture (excluding abandonments).
Durham are now third on nine points and cannot catch the Red Rose. But they can still finish as one of the best two third-placed qualifiers should they beat Nottinghamshire at Trent Bridge on Sunday.
Lancashire host Leicestershire here as they bid to finish as the best second-placed team for a home tie.
Opener Lees anchored the Durham innings after they had elected to bat, hitting only three boundaries in his 60 balls and showing the composure no one else could.
Any thoughts of him being on the slow side were quickly dispelled by Potts' early brilliance on the same pitch used for Wednesday's ODI between England and Australia and last night's Roses clash.
Graham Clark, the ball after hitting a six, Ben Raine and David Bedingham all holed out into the leg-side as the visitors slipped to 47 for 3 in the sixth over, with Luke Wood, Danny Lamb and Saqib Mahmood all striking.
Durham had been 40 for 1 after four overs before Lancashire's renowned pace-off-the-ball tactics through the middle of the innings dragged things back.
Seamer Lamb mixed his pace and was the pick of the Lightning attack with 1 for 15 from three overs, getting Raine caught at deep mid-wicket (43 for 2 in the fifth).
Earlier, Dane Vilas took a superb one-handed catch diving backwards at mid-on to help left-arm quick Wood get rid of Clark. Wood finished with two wickets in two overs.
Former South African international Farhaan Behardien chipped in with a run-a-ball 26, sharing 61 inside 10 overs for the fourth wicket with Lees.
Brydon Carse then played as aggressively as anybody for 23 off 15 balls, including a straight four and slog-swept six off successive Matthew Parkinson deliveries in the 17th over as the score moved to 130 for four.
A couple of overs earlier, left-handed Lees had reached his fourth Blast fifty this season - and his second against the Lightning - off 45 balls.
Lancashire's chase then got off to the most disastrous start as they lost Alex Davies, Steven Croft, captain Vilas and Rob Jones in the first two overs - the latter three all to ducks.
Davies struck two early boundaries before miscuing left-arm spinner Liam Trevaskis to mid-off five balls into the innings.
Then came Potts' unbelievable first over as he forced Croft to miscue a pull to short mid-wicket (Lees the catcher), trapped Vilas lbw and uprooted the off-stump of Jones.
In Wednesday's win against Yorkshire at Emerald Headingley, the 21-year-old took three wickets in his first two overs.
Livingstone looked to have broken the shackles by muscling Paul Coughlin for successive leg-side sixes in the fifth over, only to lose his leg-stump with the next ball as the score fell to 34 for five after 4.5 overs.
As he departed, Livingstone seemed to get into a verbal exchange with the celebrating Durham players, resulting in umpires Steve O'Shaughnessy and James Middlebrook adding five penalty runs to Lancashire's target.
With that, it was all but game over.
Scott Steel's off-spin claimed the wickets of George Lavelle and Luke Wood - the latter bowled with a beauty - in the eighth over (48 for seven).
Trevaskis returned to bowl Tom Hartley in the ninth before Steel had Mahmood caught in the deep in the 12th (66 for 9) to finish with a career-best 3 for 20.
Lamb added a consolatory 29 not out before Parkinson chipped Nathan Rimmington to cover to wrap things up.