A win under the Derby floodlights tonight will book Durham's place in the Twenty20 quarter-finals following last night's thrashing of Yorkshire at Riverside.
Durham's 162 for eight was three more than the sides managed in their tied match at Headingley on Sunday and always looked too many as the Tykes' decision to field first backfired badly in fading light.
Yorkshire's first-time opener Adil Rashid was run out in the first over without facing a ball, setting the scene for a batting display almost as dismal as the light.
After making only six off the first two overs, when visibility was still good, Yorkshire struggled to 49 for five after ten overs before rain ended play and Durham were declared the winners by 39 runs under the Duckworth/Lewis method.
Yorkshire were handed a lifeline by Nottinghamshire losing to Leicestershire, but will probably have to win both their remaining group games, at home to Leicestershire tomorrow and at Trent Bridge on Friday, to reach the last eight.
Barring the same trouble they had with the light in their Friends Provident match at Derby, Durham will expect to win tonight. Home advantage in the quarter-finals could then hinge on Friday's home game against Lancashire, when they will hope to exceed last night's crowd of 4,923.
After losing the toss for the 13th time in 15 one-day games, Durham were required to bat first for the first time in this season's Twenty20.
Yorkshire's strength tilted even further towards their bowling with the news that England had requested that Michael Vaughan should be rested. As the first Test against South Africa is more than two weeks away this seemed unnecessarily cautious and came just when the player was beginning to find his feet in this competition following his top score of 34 against Durham on Sunday.
Vaughan will apparently be available for the championship match against Durham starting at Headingley on Sunday.
He might not have been keen to bat in last night's gloom. The light was deteriorating rapidly at the start of Yorkshire's innings and by the time they were 29 for four in the seventh over it was only the white ball which made visibility possible.
Phil Mustard launched Durham's innings with 49 off 37 balls, including two sixes. He picked up Matthew Hoggard behind square for six in the third over as he and Michael Di Venuto shared the runs equally in an opening stand of 35 in five overs.
Di Venuto then edged to wicketkeeper Gerard Brophy when trying to pull Tim Bresnan and Mustard was briefly starved of the strike.
But Will Smith hit both Hoggard and Bresnan in front of mid-wicket for four before Rashid came on with the total on 48 after seven overs.
Durham had again chosen not to play their leg-spinner, Scott Borthwick, and when Rashid dropped his fifth ball short Smith pulled him for six.
Mustard had added only four singles in the previous three overs but immediately swept Richard Pyrah for four when the medium pacer replaced Hoggard.
Mustard then lifted Rashid over long-on for six and edged him for four, but Smith departed for 20 in the 11th over when a fierce drive off Pyrah was brilliantly held by Rashid at extra cover.
For the third successive innings Mustard fell in the 40s when he skied Pyrah to Brophy to bring in Albie Morkel at 97 for three in the 13th over.
He was able to begin quietly as Dale Benkenstein was in full flow at the other end, taking 16 off Darren Gough's first over.
The Durham captain had begun by flipping Pyrah just short of the rope at fine leg and when Gough's attempted in-swinging yorkers failed to hit the mark he was driven through extra cover for four and picked up behind square for six.
But with a total of 180 beckoning Durham lost their way as their South Africans all departed in the next three overs. Benkenstein lofted Pyrah's slower ball to long-on, Morkel edged Gough to Brophy and Shaun Pollock was run out when Gareth Breese declined a second run to deep backward square leg.
Only 13 runs came off three overs at that point, but rather than risk Rashid, Gough turned to Anthony McGrath for the 19th over, which cost 14 even though he had Liam Plunkett stumped.
Garry Park scooped McGrath's last ball over his left shoulder for three, but an excellent last over by Gough yielded only six, which included two byes to the wicketkeeper and an overthrow.
Brophy's five victims counted for little when he walked across his stumps and was bowled by Pollock in the third over to leave Yorkshire on nine for two. He had already declined Rashid's call for a second run and seen him stranded by Steve Harmison's throw.
With rain starting to fall, the competition's leading run scorer, McGrath, drove Plunkett to Ben Harmison at extra cover in the sixth over and all hope was gone for Yorkshire.
Steve Harmison bowled Adam Lyth and Bresnan edged to Mustard to give Harmison his eighth wicket in three games.
Jacques Rudolph was on 22 when a combination of rain and bad light brought proceedings to an unsatisfactory end at 8.10.
This cast doubt on the wisdom of Durham starting these games at 6pm, 30 minutes later than elsewhere, and the ECB have decreed that all the final group games on Friday will start at 5.30.