Emerging opener Tom Smith improved his best score in Twenty20 cricket for the second successive game as Lancashire reeled off a sixth straight win.
Smith hit an unbeaten 57 out of Lancashire's 124-4 as they beat Durham with five balls to spare.
Earlier Durham opener Gordon Muchall had batted though for 50 out of 123-6.
North division leaders Lancs have now all but qualified for the last eight as they take a maximum 12-point haul going into the competition's 18-day break.
Lancashire are now four points clear of second-placed Yorkshire and six clear of the pack.
And, with two of the best third-placed finishers from each group to qualify for the quarter-finals, it would take an extremely unlikely turn of events to deny Lancashire a safe passage to the last eight now.
They resume action with a home tie against Leicestershire at Liverpool on Monday 22 June (1730 BST).
And Liverpool-born opener Smith could not be going back to his native city in better form after another highly promising knock.
The young man, who is keeping the fit-again Mal Loye out of Lancashire's all-conquering side, hit a six and four fours in his unbeaten 57 off 56 balls.