Durham 154 for 7 (Smith 37*, Zahir 2-19) beat Lancashire 150 for 9 (Davies 53, Trevaskis 4-16) by four runs
Liam Trevaskis a part-time left-arm spinner from Carlisle, took three wickets in a brilliant last over as Durham once again proved their ability to scramble wins from unpromising situations as they snatched a startling victory against Lancashire at Emirates Old Trafford.
Trevaskis, 19, who had taken only one wicket in seven previous T20 appearances, defended just six off the last over and finished with a career-best four for 16 as Lancashire chased a 155 target, slipping badly from a position of strength at halfway.
He conceded only one in the last over as he had James Faulkner caught at long-on, Lamb stumped and Matthew Parkinson caught at deep midwicket. The Lightning needed 63 off the last 10 overs with six wickets left and finished on 150 for nine.
It was another blow for Faulkner, Lancashire's Australian allrounder, who is attempting to rebuild his reputation after his career was blighted by injury.
Trevaskis made his T20 debut last season, dismissing England's Alex Hales in the match against Nottinghamshire at Chester-le-Street and also played for England's Under-19 side in the One-Day series with India.
Durham's four-run win significantly strengthens their hopes of quarter-final qualification. The second-placed Jets have moved to 14 points from 10 games, one behind leaders Worcestershire. Lancashire are fourth on eleven points from 10. Durham, assumed to be also-rans, are proving more resilient then many deemed possible.
"I'm still a little bit lost for words on how we actually came out victorious," said Durham captain Tom Latham. "James Weighell was going to bowl the last over, but it looked easier with pace on the ball and Liam had bowled a good couple of overs beforehand. He hasn't played a huge amount of T20 cricket, and his main role is as a batter."
Earlier, Lancashire's Afghanistan spinner Zahir Khan impressed with 2 for 19 on his debut on an Old Trafford pitch again prepared with slow bowlers in mind.
Durham posted 154 for 7, a total which looked under par when Alex Davies flew out of the blocks in reply with 53 off 33 balls.
Zahir, also 19, has signed for the rest of the season on Jos Buttler's recommendation having been squad mates at Rajasthan Royals in the IPL earlier this summer. He bowled considerably more googlies than chinamen in a mid-innings spell that seemed to have made Lancashire strong favourites.
Trevaskis was bowled around his legs as he tried to sweep and veteran Paul Collingwood fell lbw sweeping in an eye-catching four-over spell.
Durham started positively with the bat, reaching 56 for 1 in the seventh over. But they stumbled through the middle in the face of Khan and Lamb, whose sister Emma also struck twice in a Kia Super League game earlier in the day.
In the end, the Jets did well to get up to 154 as veteran Will Smith hit three sixes in 37 not out. Their innings included nine sixes and only six fours.
Danny Lamb had James Weighell caught at deep cover off a full toss and Stuart Poynter caught at mid-off in only his second Blast appearance of the summer and third in all. Earlier, Jordan Clark caught younger brother Graham at long-on for 29 off leg-spinner Matthew Parkinson.
Chris Rushworth had Karl Brown caught at mid-on in the first over of the Lightning chase, but Davies quickly found his range on the way to a club record equalling fifth Blast fifty of the season.
Davies found useful support from pinch-hitter Arron Lilley (28). They shared 72 inside eight overs for the second wicket before Lilley was run out to leave the score at 78 for two in the eighth.
Davies reached his fifty off 32 balls in the 10th over, but he was caught behind off Ben Whitehead's leg-spinners with his next ball - 88 for three.
Steven Croft miscued a return catch to Trevaskis as Lancashire's target became 41 off the last six overs. Whitehead struck again to remove Dane Vilas as the game tightened up significantly to 19 off two overs. Jordan Clark fell to Nathan Rimmington in the penultimate before Trevaskis had the final say.
Lancashire face Yorkshire at Emerald Headingley on Thursday evening, while Durham host Leicestershire on Wednesday in a busy week that could decide their season.