An under-strength Yorkshire side suffered a Vitality Blast Roses defeat by six wickets at Emerald Headingley to significantly dent their quarter-final hopes.
The Vikings were missing Matthew Fisher, Tom Kohler-Cadmore, Josh Poysden and captain David Willey due to a Coronavirus related issue.
And, unfortunately, the second-placed Lightning took advantage to move four points clear of the Vikings with three games remaining as both sides bid to seal a last-eight berth.
Yorkshire slipped from 62-1 after six overs, having elected to bat, to 145-9, with Matthew Parkinson and Luke Wood claiming three wickets apiece and stand-in captain Adam Lyth top-scoring with 36.
Captain Dane Vilas top-scored for the visitors, who slipped to 77-4 in the ninth over of their chase, with 44 not out off 36 balls as the victory was sealed with 2.1 overs remaining.
It now means the Vikings are likely to have to win their three remaining games to have any chance of qualifying, even with the cushion of knowing the two best third-placed finishers from the North, Central and South Groups also advance to the quarter-finals.
Dawid Malan’s return from England duty was off-set by the absence of Kohler-Cadmore and Willey, and that told as the hosts stumbled following a rapid start – 30-0 after two overs and 62-1 after six.
Openers Harry Brook and Lyth both pulled huge sixes into the Western Terrace before Lancashire squeezed with spin through the middle of an innings which included some ragged fielding.
They dropped three catches in all, with Tom Bailey the culprit twice. Lyth was dropped twice.
Leg-spinner Parkinson striking twice in his first three balls to remove Malan for 27 and former England Under 19s all-rounder George Hill, leaving Yorkshire at 87-4 in the 11th over, was the the key moment in the fixture.
Earlier, Brook (17) was the first wicket to go in the third over, brilliantly caught by a diving Tom Hartley running around from short third-man off left-arm quick Wood – 30-1.
Malan, a reserve player in England’s bubble for the ODI series against Australia, was released to make his Yorkshire T20 debut and played nicely.
However, after Lyth was stumped off Hartley’s left-arm spin, Malan was the first of the two wickets to fall in Parkinson’s first over when he was caught at deep mid-wicket on the slog sweep for 27. Two balls later, Hill chipped to cover – 87-4.
Wickets continued to fall at key intervals.
Nineteen-year-old Academy batsman James Wharton, drafted in for his first-team debut, was caught at cover off Parkinson – 104-5 in the 15th.
Mat Pillans was stumped off Liam Livingstone’s leg-spin almost two overs later as the score fell to 121-6, with the last five wickets all falling to spin.
Wood then returned to strike twice in the 17th over.
He trapped Jordan Thompson lbw and had Will Fraine caught behind for 24 – 124-8 – before Danny Lamb removed Ben Coad in the last over of the innings.
Pillans and Thompson then removed Lightning openers Livingstone and Alex Davies, caught behind and caught at deep square-leg respectively, as the visiting chase fell to 35-2 in the fourth over.
And the departures of Steven Croft, run out following a mix-up with Vilas, and Josh Bohannon, bowled by Coad via inside-edge, left the score at 77-4 in the ninth.
But Lancashire’s run-rate was good, and Vilas and Rob Jones calmed things down and shared an unbroken 71 inside 10 overs for the fifth wicket.
Jones finished unbeaten on 38, and Yorkshire are now without a Roses victory in the Blast since August 2017.
That is something they will want to end at Emirates Old Trafford on Thursday. Before then, the Vikings face Durham here on Wednesday evening (6.30pm).