Liam Trevaskis took three wickets in a brilliant last over as Durham snatched a Vitality Blast victory from the jaws of defeat against Lancashire at Emirates Old Trafford.
The 19-year-old left-arm spinner defended just six off the last over and took his first wickets of the campaign, finishing with four for 16 from his four overs in a four-run win.
Lancashire, chasing 155, slipped badly from 92 for three at halfway as they finished on 150 for nine.
Durham move to 14 points from 10 games, one behind leaders Worcestershire. Lancashire are fourth on 11 points from 10.
Earlier, Lancashire's Afghanistan spinner Zahir Khan impressed with two for 19 on debut as Durham posted 154 for seven, a total which looked under par when Alex Davies flew out of the blocks in reply with 53 off 33 balls.
Trevaskis said: "It was good to come out on the winning side. It can go both ways in that situation.
"I'd bowled a touch full in the few overs I'd bowled, so I dragged my length back.
"We're in a good position, and hopefully we can secure that spot and hit the quarter-finals."
Glamorgan climbed to third place in the Southern Group after a six-run Vitality Blast victory over Essex at Sophia Gardens gave them a fourth successive win.
Colin Ingram struck 89 from 47 balls for Glamorgan before Graham Wagg (53 not out) and Ruaidhri Smith (22no) plundered 60 runs from the final three overs to carry the Welsh county to 198 for seven.
Varun Chopra hit a half-century of his own in the reply - 54 off 41 balls - but they were left needing 24 off the final over.
Ravi Bopara gave them hope striking 16 off the first four deliveries but he could only score one off the final two, finishing unbeaten on 45 as Essex closed on 192 for six.