Victory and favourable results elsewhere, particularly Hampshire defeating Essex, could have seen the Dynamos claim a berth in the last-16 as a best-placed third.
But despite restricting Lancashire to 133-8, the Dynamos could only muster five from the final over as Gareth Breese was run out from the final delivery with one run required.
Head Coach Cook said: “Ultimately it is very disappointing, we had a chance to go through today and we played well in patches, but we showed that there are some aspects of the game where we have to nail down.”
Lancashire got off to a solid start through Stephen Moore and Tom Smith.
After Moore was clean bowled by Chris Rushworth (2-19), Lancashire added impetus and reached 70 before the introduction of spin reaped rewards for the Dynamos.
Scott Borthwick (2-19) and Breese (2-15) turned the screw to restrict the flow of runs and crucially pick up the wicket of Smith (29), as well as Paul Horton and then Yasir Arafat for single-figures.
After being 74-2 at the halfway stage, the Dynamos would have been pleased to restrict Lancashire to just 60 from the second half of their innings.
With talk of net run rate being key to the Dynamos’ progression, Phil Mustard and Herschelle Gibbs looked for early momentum, but found boundaries hard to come by as Glenn Chapple conceded just 10 runs from his alloted four overs.
Gibbs fell LBW to Chapple, and Mustard was joined by Ben Stokes who hit two fours and a six in his 26.
Once Mustard (33) had departed to a simple caught and bowled chance for Gary Keedy, the Dynamos required 55 from the remaining seven overs but the losses of Johann Myburgh and Gordon Muchall set up a tense finale.
With the Dynamos requiring six runs from the final over, and four runs scored from the first three deliveries, victory appeared a certainty.
But Dale Benkenstein (28) was caught and Breese looked to clinch the final run from the final delivery, but Horton hit the stumps and the scores were left level.
Cook added:”Consistency has been the biggest thing, we have won four, tied one, and lost four.
“There has been positives, Herschelle has brought a lot of knowledge to the dressing room, Scott Borthwick has bowled well too, so we can take positives we just need to improve other key areas.”
Match report courtesy of Chris Woods.